because some people cannot be trusted, it's a fact of life.

self defence mechanism

It's very difficult question. Give us examples, please

I think it s hard to trust people cause if you were just for once lied you ll remember and this is going to make you think that other people can be the same.If you re lied many times you ll lose your trust in people.If you stay with people who don t lie you you ll have a better trust.