I read the first chapter of "A Brief History Of Time" when Dad was still alive, and I got incredibly heavy boots about how relatively insignificant life is, and how, compared to the universe and compared to time, it didn't even matter if I existed at all.
When Dad was tucking me in that night and we were talking about the book, I asked if he could think of a solution to that problem.
"The problem of how relatively insignificant we are."
He said, "Well, what would happen if a plane dropped you in the middle of the Sahara Desert and you picked up a single grain of sand with tweezers and moved it one millimetre?"
I said, "I'd probably die of dehydration."
He said, "I just mean right then, when you moved that single grain of sand. What would that mean?"
I said, "I dunno, what?"
He said. "Think about it."
I thought about it and I said, "I guess I would have moved a grain of sand."
"Which would mean?" he asked again.
"Which would mean I moved a grain of sand?" I replied.
"Which would mean you changed the Sahara." said Dad.
"So?" I confused.
"So?. So the Sahara is a vast desert. And it has existed for million of years. And you changed it!" explained Dad.
"That's true!" I said, sitting up. "I changed the Sahara!"
"Which means?" he said.
"What? Tell me." I became so excited.
"Well, I'm not talking about painting the Mona Lisa or curing cancer. I'm just talking about moving that one grain of sand one millimetre." said Dad again.
"If you hadn't done it, human history would have been one way ..." told Dad to me.
"But, you did do it, so ...?" Dad said it and smiled.
I stood on the bed, pointed my fingers at the fake stars, and screamed: "I changed the universe!"
"You did." Dad laughed.
Source: "Extremely Loud & Incredibly Close" by Jonathan Safran Foer