It is true that when we people with bad intentions we usually imagine that all other people are the same. However, we should not do it since all are not as we think, wise words expressed by your friend and it is very accurate, I personally understood it and that over the years you realize that it is like that and you are leaning on them to build that trust, and not allow as you expressed that those situations change your personality, we just have to be smart and be aware of those situations.