Walking through the parking lot to the store, I saw a crumpled soft drink can. It was at the far end of a parking space and I wanted to pick it up, but... well, it would be awkward to walk into the space just to pick up the can, then walk all the way back to the car (four or five spaces) to stow it.
So I didn't.
Yes, it was only a can and it was worth about a penny; it was also a tiny bit of a natural resource that is lost every day, but I still kicked myself later (figuratively!) for not taking a few seconds to pick it up.
How often do we do things like that? Maybe not aluminum cans, but maybe buying a mix for cornbread, when cornmeal, milk and baking powder are already on hand, or not bothering to turn off the water when we're brushing our teeth.
Things that seem very small add up quickly. Sometimes the reason they seem very small is that the time it takes to do them is very small. If the aluminum can had taken 10 seconds to pick up, that adds up to about 6 cents a minute, which adds up to $3.60 an hour. That's hardly a living wage, but I wouldn't complain if $3.60 was added to every hour I spend doing anything.
What I'm saying is that it's not like we have to make great or sustained efforts to create these bits and pieces of monetary enrichment, so why not? Why "leave money on the table" when we don't have to?
If you're fixated on aluminum cans now, read How to Pick Up Cans for Fun and Profit. It will encourage you!