They are very important (if you want people to like and think well of you) and hard to change. The human brain is hardwired to evaluate a person within the first 30 seconds of meeting them, and is involuntary. Everyone does it and you can't stop it. It was originally a survival instinct; you could never tell if someone approaching you was friend or foe and could mean the difference between life and death. Of course they aren't made in that sense nowadays, considering our circumstances have changed since those times. Now they're used to evaluate the information to make judgement calls.