Why do people dont choose best answer?

It really pisses me off!!that i try hard to find the answer to a person's question and they just dont choose a best answer!Like last time i honestly thought i was suppost to get the best answer but the asker never choose the best answer!So when i saw that it was in voting i forgot to choose my self so then i saw it was resolved and the best answer was a sucky answer!!Mine was way better!...so what i mean is that people with not that good of answers will vote for themselves!People dont forget to choose best answers!...what do you guys think of this?and why wont people choose best answer!