No one has an incentive to tell you hard-hitting uncomfortable truths about yourself that you are blind to. Giving hard feedback is an awkward confrontational situation—to the person giving feedback and the person receiving feedback. We avoid confrontation with people we know.
This behavior(avoiding face to face confrontation) of ours might have something to do with evolution. In the yesteryears, co-operation was essential for survival.
If you are stupid or your idea is ridiculous, no one is going to tell it to your face; they might give you hints.
Giving hard feedback takes effort. We feel these things; it is tough to verbalize. It is tougher to convey it in a way that does not offend the other person. There is nothing to gain for the person giving the feedback by putting in the work. It is an asymmetric situation.
When you ask others for feedback, most of the time, the other person knows what you want to hear. We hardly have a neutral position on anything. When we bounce ideas with others, we are after confirmation, asking them to endorse the thought rather than poke holes in it.
This is also why we find it tough to say no or why you hardly hear no from others. I am not talking of abject strangers but someone familiar. Saying no is awkward. When we say no, we believe we have to justify it. Nos are feelings; we find it hard to verbalize them. When we say no, it is a confrontational situation that we want to avoid. Hence we sidestep the situation by staying silent or saying yes and not doing it later.
When you meet someone who gives you hard feedback or says no to your face, keep that person close to you and thank your stars.