"It is better to remain silent and be thought a fool, than to open one's mouth and remove all doubt." -Abraham Lincoln.
Dialogue for a video game protagonist is a double-edged sword. Develop them into a three dimensional character and you'll risk alienating your audience who may not like them. A common workaround is to leave the protagonist silent so the player can impart their own identity unto their avatar.
The problem here is often one-sided conversations feel awkward. Just look at Gordon Freeman, silent hero of the Half-Life series for example.