- You have to push this button.
- You have to just push this button.
What role does the word 'just' play in the sentence above?
just is suggesting an exact idea of how to do something.
The Oxford English Dictionary has a definition:
Exactly, precisely; verily, actually; closely
Without it, it's simply a blunt command to do something.
With it, it's proposing a specific task that will precisely accomplish what's needed.
Just kill him!