Believing Things

Today I realized that it seems like often people choose to believe or disbelieve things in a completely irrational manner.
A teenage girl told me this week that she didn't believe in the big bang because scientists just say "it happened." I didn't deny that this is what they say... but I think they say it because (in my non-expert opinion) it seems like they don't know all the answers, but the answers they do know are so complicated that a girl in junior high just wouldn't have the background to understand the answer if they did try to explain it.
I also recently heard someone say that they didn't have any idea how cell phones work, they are just grateful they do.
My nephews after countless warnings to not touch cacti (and having done so themselves in the past) insisted on doing so again only to get a hand full or spines instead.
I just looked for random facts on google, and found this one "There are 336 dimples on a regulation golf ball."

Sometimes we can't understand things so we believe them to be false (like the teenage girl).
But sometimes we can't understand things and we just take it for granted (like cell phones).
Sometimes things are simple and ordinary and yet we still can't quite take someone else's word for it... or even our own (like my nephews).
But sometimes things are not ordinary and we have no understanding to base even an assumption on but we believe them anyway, for no reason, except that someone else said it (golf balls).

So we don't always believe things just because they are ordinary, or extraordinary. We also don't believe things just because we have first hand knowledge or have no knowledge of the subject. So really why do we believe some things and not others?