Because the writing system just ain't very phonetic.因为书写系统并不太与其发音对应。

So much for the physical process of writing the characters themselves. What about the sheer task of memorizing so many characters? Again, a comparison of English and Chinese is instructive. Suppose a Chinese person has just the previous day learned the English word "president", and now wants to write it from memory. How to start? Anyone with a year or two of English experience is going to have a host of clues and spelling rules-of-thumb, albeit imperfect ones, to help them along. The word really couldn't start with anything but "pr", and after that a little guesswork aided by visual memory ("Could a 'z' be in there? That's an unusual letter, I would have noticed it, I think. Must be an 's'...") should produce something close to the target. Not every foreigner (or native speaker for that matter) has noted or internalized the various flawed spelling heuristics of English, of course, but they are at least there to be utilized.

Now imagine that you, a learner of Chinese, have just the previous day encountered the Chinese word for "president" (总统 zǒngtǒng ) and want to write it. What processes do you go through in retrieving the word? Well, very often you just totally forget, with a forgetting that is both absolute and perfect in a way few things in this life are. You can repeat the word as often as you like; the sound won't give you a clue as to how the character is to be written. After you learn a few more characters and get hip to a few more phonetic components, you can do a bit better. ("Zǒng 总 is a phonetic component in some other character, right?...Song? Zeng? Oh yeah, cong 总 as in cōngmíng 聪明.") Of course, the phonetic aspect of some characters is more obvious than that of others, but many characters, including some of the most high-frequency ones, give no clue at all as to their pronunciation.
现在想象你一个学习中文的,昨天刚刚碰到中文里的president“总统”。现在你想写它。你如何回忆起这个词儿呢?首先呢,你 (很可能)已经忘掉怎么写了,生活中很少能忘得如此彻底和干净…… 你可以尽情地重复学习这个词,而发音绝不会帮助你记起如何书写。当你学了较多汉字,掌握一些发音构件的规则时可以情况会好些。(“总”有时出现在其他汉字里,也发类似的音,对吧?Song?Zeng?对了!“总”在“聪明”里有。)当然有些发音的构件要更明显一些,不过很多汉字,包括一些最常见的高频率汉字,对它们的读音完全不给任何线索。

All of this is to say that Chinese is just not very phonetic when compared to English. (English, in turn, is less phonetic than a language like German or Spanish, but Chinese isn't even in the same ballpark.) It is not true, as some people outside the field tend to think, that Chinese is not phonetic at all, though a perfectly intelligent beginning student could go several months without noticing this fact. Just how phonetic the language is a very complex issue. Educated opinions range from 25% (Zhao Yuanren)7 to around 66% (DeFrancis),8 though the latter estimate assumes more knowledge of phonetic components than most learners are likely to have. One could say that Chinese is phonetic in the way that sex is aerobic: technically so, but in practical use not the most salient thing about it. Furthermore, this phonetic aspect of the language doesn't really become very useful until you've learned a few hundred characters, and even when you've learned two thousand, the feeble phoneticity of Chinese will never provide you with the constant memory prod that the phonetic quality of English does.

Which means that often you just completely forget how to write a character. Period. If there is no obvious semantic clue in the radical, and no helpful phonetic component somewhere in the character, you're just sunk. And you're sunk whether your native language is Chinese or not; contrary to popular myth, Chinese people are not born with the ability to memorize arbitrary squiggles. In fact, one of the most gratifying experiences a foreign student of Chinese can have is to see a native speaker come up a complete blank when called upon to write the characters for some relatively common word. You feel an enormous sense of vindication and relief to see a native speaker experience the exact same difficulty you experience every day.

This is such a gratifying experience, in fact, that I have actually kept a list of characters that I have observed Chinese people forget how to write. (A sick, obsessive activity, I know.) I have seen highly literate Chinese people forget how to write certain characters in common words like "tin can", "knee", "screwdriver", "snap" (as in "to snap one's fingers"), "elbow", "ginger", "cushion", "firecracker", and so on. And when I say "forget", I mean that they often cannot even put the first stroke down on the paper. Can you imagine a well-educated native English speaker totally forgetting how to write a word like "knee" or "tin can"? Or even a rarely-seen word like "scabbard" or "ragamuffin"? I was once at a luncheon with three Ph.D. students in the Chinese Department at Peking University, all native Chinese (one from Hong Kong). I happened to have a cold that day, and was trying to write a brief note to a friend canceling an appointment that day. I found that I couldn't remember how to write the character 嚔, as in da penti 打喷嚔 "to sneeze". I asked my three friends how to write the character, and to my surprise, all three of them simply shrugged in sheepish embarrassment. Not one of them could correctly produce the character. Now, Peking University is usually considered the "Harvard of China". Can you imagine three Ph.D. students in English at Harvard forgetting how to write the English word "sneeze"?? Yet this state of affairs is by no means uncommon in China. English is simply orders of magnitude easier to write and remember. No matter how low-frequency the word is, or how unorthodox the spelling, the English speaker can always come up with something, simply because there has to be some correspondence between sound and spelling. One might forget whether "abracadabra" is hyphenated or not, or get the last few letters wrong on "rhinoceros", but even the poorest of spellers can make a reasonable stab at almost anything. By contrast, often even the most well-educated Chinese have no recourse but to throw up their hands and ask someone else in the room how to write some particularly elusive character.
事实上,这种经历如此令人宽慰,以至于我干脆记了一个单子,上面列着我看到的中国人提笔忘掉的汉字(提笔忘字?)(一个有病的,强迫症的行为,嗯我自己也知道……)。我见过很有学问的中国人忘掉如何书写“罐头”的“罐”,“膝盖”的“膝”,“改锥”的“锥”,“捻拇指”的 “捻”,“胳臂肘”的 “肘“,“姜”,“垫子”的“垫”,“鞭炮”的“鞭”,等等。我说的忘,指的是他们常常连第一笔画都不知道怎么写。你能想象一个教育良好的英语人士完全不会书写“膝盖”或者“罐头”么?(译者注:分别是knee和tin can)或者哪怕“scabbard”或“ragamuffin”这种少见的词,他们也不会忘。我有一次和三个北京大学中文系的三个博士生吃午饭,他们三个都是中国人(一个来自香港)。我那天正好感冒,打算给一个朋友写个纸条取消我们一个约会。我发现自己想不起来怎么写“喷嚏”中的“嚏”了。于是我问那三位该怎么写。结果吓我一跳,他们仨都尴尬而难为情地耸耸肩。谁都不能正确地写这个字儿。各位同学!北京大学常常被认为是中国的哈佛啊。你能想象三个哈佛大学英文系的博士生不会写“sneeze”(喷嚏)?然而这种情况在中国绝不少见。英文就是大大地比中文容易书写和记忆。不管这个词频率多低,拼写多奇怪,英语人士总能整出点儿什么来,就是因为拼写和发音是有一定对应关系的。你可能不记得“abracadabra”里面有没有连接符,或者“rhinoceros”最后几个字母不会拼,但最糟的家伙也能差不多点儿的拼出来几乎任何词。与此相反,即使是教育最好的中国人在写某些特别难记的汉字时也可能束手无策,只能问问别人。

As one mundane example of the advantages of a phonetic writing system, here is one kind of linguistic situation I encountered constantly while I was in France. (Again I use French as my canonical example of an "easy" foreign language.) I wake up one morning in Paris and turn on the radio. An ad comes on, and I hear the word "amortisseur" several times. "What's an amortisseur?" I think to myself, but as I am in a hurry to make an appointment, I forget to look the word up in my haste to leave the apartment. A few hours later I'm walking down the street, and I read, on a sign, the word "AMORTISSEUR" -- the word I heard earlier this morning. Beneath the word on the sign is a picture of a shock absorber. Aha! So "amortisseur" means "shock absorber". And voila! I've learned a new word, quickly and painlessly, all because the sound I construct when reading the word is the same as the sound in my head from the radio this morning -- one reinforces the other. Throughout the next week I see the word again several times, and each time I can reconstruct the sound by simply reading the word phonetically -- "a-mor-tis-seur". Before long I can retrieve the word easily, use it in conversation, or write it in a letter to a friend. And the process of learning a foreign language begins to seem less daunting.

When I first went to Taiwan for a few months, the situation was quite different. I was awash in a sea of characters that were all visually interesting but phonetically mute. I carried around a little dictionary to look up unfamiliar characters in, but it's almost impossible to look up a character in a Chinese dictionary while walking along a crowded street (more on dictionary look-up later), and so I didn't get nearly as much phonetic reinforcement as I got in France. In Taiwan I could pass a shop with a sign advertising shock absorbers and never know how to pronounce any of the characters unless I first look them up. And even then, the next time I pass the shop I might have to look the characters up again. And again, and again. The reinforcement does not come naturally and easily.