As an adverb, 就 (jiù) can be placed before the predicate to add emphasis. It often has an intense or provocative feel it it, like how we sometimes say in English "it's just not right!", or other similar phrases. It often appears as 就是.

Structure
It's as simple as putting 就 in front of a verb.

Examples

Wǒ jiùshì bú rànɡ nǐ qù.
我就是不让你去。
I'm just not going to let you go.