There are Indian religious schools that teach about karma. Westernized the concept is simplified as a rule of cause and effect, reaping what you're sowing, doing good and therefore experiencing good and vice-versa doing bad and experiencing bad.
There is also: good karma, bad karma and neutral karma (not to be neglected, you don't have to be all good and some good can even be bad, think helper-syndrome and/or self-exploitation).
I like to think it exists or not rule it out. It gives my life more meaning to believe in it.
I like to "collect" good karma sometimes by doing little good things or I think of karma sometimes when I do them in everyday life. Don't get me wrong. I'm not an especially good person. I have been working hard on myself in the last couple of months though.
One thought I had recently that felt very good is that I can quickly gain good karma if I want to by not only treating others well or fairly but also by treating myself well. I'm someone. My needs have to be taken care of. Doing that job and doing right by myself is a good deed. It should align with the rules of karma especially when self-care requires effort sometimes. This helps me trick self-neglect sometimes. I wanna practice such thoughts more.