This can lead to seeing and believing that things are the way we want them to be, but it also can cause us to see what we are afraid of (as in paranoia), or just what we have gotten in the habit of seeing. Any textbook on psychology will have examples. Look under "cognitive dissonance". This lack of contact with reality is what Buddhism means by "ignorance". It is a problem because reality feels no obligation to live up to our ideas about it. If we are emotionally attached to the idea of things being permanent, even though we know better intellectually, then when things break, in addition to the natural regret, we feel betrayed and offended! It wasn't "supposed to" do that!