Ok, how about this. There is a giant pit, and a giant mountain with some gold in it. Miners come and try to find this gold by breaking a piece of rock off. The rock is hard and not easy to break free, so it takes a lot of work to remove a pebble.  

Each miner breaks a pebble off the mountain and throws it in the pit with their unique code. Every now and then, after about 3 trillion pebbles, a miner finds a rock made of gold, and throws that into the pit. When this happens, a machine scans each piece of rock in the pit and gives credit to the miner who threw it in, based on how many pebbles they added and the total pebbles added by all miners.

Instead of just awarding the pebbles they added between now and the last time a gold pebble was added, the machine looks back at the last 15 trillion pebbles added by everyone, and pays them for that work too.

If a miner could add 100 pebbles per day, and started adding them right now, but a gold pebble was found 2 days after they started, looking at the last 15 trillion pebbles, it would average that they were adding less than 100 pebbles per day because so much of the other pebbles were from others. Over time, as the miner added more pebbles, the portion of the last 15 trillion that were added by them would equal the number they produce per day.

This is similar to how the pool works.