I pride myself on being a modern, rational person. I'm not religious or spiritual (I don't look down on and actually envy a bit people who are, but I am not and it's just not something I can will myself to be) and definitely not superstitious. I don't throw salt over my shoulder, knock on wood, or freak out if a cat crosses my path or I walk under a ladder. I have few rituals in my life that explicitly deal with luck (though I have noted a tendency toward OCD on occasions, especially when I'm stressed, it's really not the same thing).
There is an older woman who lives down the block from us, and many mornings on my way to work I will see her walking to church. Sometimes she walks past me and says hello, but most of the time she will randomly veer off the sidewalk, walk around cars, and essentially pick a strange and circuitous route like a child might do. My wife and I sometimes joke that she is compelled to do these weird things to ward off the return of Cthulhu, but the truth is that she's probably just a little nutty, in addition to very superstitious.
Despite liking to think of myself as completely materialist and rational, I find that I possess a very strong internal sense of karma when it comes to finding and losing things.
It's not just a sense of trying to be an honest person, though there's an element of that as well. It really seems more about justice, about golden-ruleness, about wanting to do everything I can to increase the likelihood that if I lose something important - say, my SmartTrip card (I found one in my building last week, and if you're not familiar with D.C. you may not know that those things can have hundreds of dollars on them, plus be monthly rechargeable) or my glasses (my wife found a pair last week) or my driver's license (I've both lost mine and found others' on more than one occasion) - that people will take the same pains to get it back to me, or at least not steal it for themselves.
If I found $50,000 in cash in a paper bag, would I turn it in? I really don't know but I'd be strongly tempted to keep it, and if I did, karma would not be among my concerns. If I found a wad of bills totaling $1,000 on the street, I'd probably keep it and chalk it up to plain old (absolutely fucking awesome) luck. But if I found a wallet with some kind of ID that had $1,000 in it, I would absolutely return it - probably by trying to get in touch directly with the person who lost it - and I wouldn't be one of those people to first take the money out and then say I'd found it empty. Nor would I expect a reward.
What it really comes down to - for me, at least - is a social compact, but one that - I notice - has me as a big part of it. I don't actually believe that were I to keep the SmartTrip card, throw out the glasses, or even strip the money out of that wallet - that it would bring bad things on me or even increase the likelihood of my losing something in the future.
That would imply some supernatural external power directing things and keeping score. And yet I can't deny that "doing the right thing" in those instances makes me feel better, even if I never know whether the person who lost the card or the glasses comes to claim them. Intuitively, even if not rationally, I embrace the concept of karma.