Why people can't handle the truth?

Because we're emotional creatures first, we default to what's familiar or comfortable. Logic/critical thinking take sustained practice and a lot of effort. There's a study that suggests that many of our conscious choices are simply post-hoc rationalizations for decisions made in the unconscious.

I absolutely no longer trust anyone that insists they're naturally and perfectly logical, they are unquestionably hiding some fixation or personal opinion which--if challenged--will make them unravel in the worst fashion.