Because you're supposed to.

So the other day I was eating a navajo taco for lunch and I was shooting the breeze with Sam, a 5th-grader.

I asked him what his favorite subject in school was, and he replied, "P.E....Physical Education...or math." I asked him why he liked math (because I sure don't), and he said, "Because you're supposed to!"

I had no reply. All I could do was laugh and accept his answer. I thought about it later and realized that sometimes there doesn't need to be more explanation than that. Sometimes we need to just accept the answers we get. Sometimes when the answer isn't what we expect, we need to just give the benefit of the doubt and trust whoever we're getting answers from.

The benefit of the doubt is that it gets easier and easier to pinpoint. Doubts force us to ask unnecessary questions, and over time that becomes painfully obvious (and annoying). Don't get me wrong, it's perfectly okay to ask questions and wonder and dream.
The benefit of the doubt is that the doubt will get stuck on the little details and get ripped off as we move forward.