Why some people are very smart yet very dumb? Seen some people get Bachelor's and Masters's degrees but throw a fit like a mentally delayed kid.

Depends on context, I have no idea what led up to you writing this. Generally however, smart people can still have biases. Smart people can be cruel or unkind or unfair or abuse people. Like someone else stated, you only go so far in education and then it gets more narrower. Adults have a hard time taking in new information which is a neuroscientific fact so at some point you become fixed in your ways even if you're wrong.