It comes from a learning- and often unfortunately a group's reinforcement of what is acceptable or not.
It helps you accept the relevance of stimuli to and in your life, given what you know at this point.
Belief requires good reasons, and although people may differ on the "good reasons." You must decide.
Read the following excerpts -
"... Now I'll give you something to believe. I'm just one hundred and one, five months and a day."
"I can't believe that!" said Alice.
"Can't you?" the Queen said in a pitying tone. "Try again: draw a long breath, and shut your eyes."
Alice laughed. "There's no use trying," she said "one can't believe impossible things."
"I daresay you haven't had much practice," said the Queen. "When I was your age, I always did it for half-an-hour a day. Why, sometimes I've believed as many as six impossible things before breakfast..."
from Lewis Carroll, Through the Looking Glass
The examples above show the dilemma of choice or acceptance of how it is - can we choose our beliefs independently?
We often hear about people preferring to believe one thing or an other, about people being inclined to believe one thing or another, and about people finding it difficult or easy to believe one thing or another.
This suggests belief is something chosen and that our choices are influenced by our desires and emotions. You would hope this to be true.
Rather, the beliefs people tend to be "proudest" of are those which they also say no one can deny.
