My dad thinks that I shouldn't trust others so easily & if I do that, I would be too naive and immatured...?

Do you agree with him? I'm way over 18 yrs old btw and I just can't agree with him on that as I would feel very uncomfortable not to be able to trust anyone... Even communication with others require trust right? If you don't trust the person you are talking to, then wouldn't those talks be just empty talks... ?