Karma is an unforgiving and unbiased force that will eventually catch up to anyone. Karma is a force that is widely believed in around the world partly because its ties to religion, however I think the main reasons karma is so widely believed is because its seems to be real. When people are kind and work hard the universe appears to be kind back and when people are on the other side of karma it always seems to catch up with them at some point.
The basis of karma is 'what you put out you get back' though the ins and outs of how it works are entirely unknown which means people can intemperate in which ever way they decide and I think that is also a big part of why karma is believed in. You can make of it what you will and people seem to like the freedom to decide how the world and universe works.
Personally I'm not fully sure on how I think karma works and I'm not even sure if it has any ties to spirituality or if it is entirely down to psychology and it could be the case that both aspects come into play. Though for today I want just look at karma as something that is entirely psychological. The spirituality of karma is something that is hard to talk about because it is not a dense solid idea, it really is a free flowing idea whereas psychology is something we know a lot about so we can build a clearer picture from it.
I think karma is a self for fulfilling prophecy at its core because it is inevitable that you will eventually become what you perpetuate to others in one way or another. Humans are natural programmed to have a survival instinct that tells us to do anything we can to survive and help our tribe survive.
Psychology:
The point I'm trying to make is that as humans we have tons of of presets that come together to create morality, though morality is not black or white because we have some many presets some can contradict each other at times because they can be situational. As I mentioned earlier we have a natural instinct to survive but we also have an instinct that tells us the needs of the many out way the needs of the few. So if it comes down to a person surviving alone or them sacrificing themselves to save the tribe they will have a difficult moral dilemma, do they live and let others die or die and let other live.
This is an extreme example but many situations with this type of dilemma regularly pop up throughout life and it can be hard to decide when your needs are more important than others or there needs are more important than yours.
This is where I think karma comes into play, if you make the decisions that your instincts don't like eventually they will be more aggressive in trying to direct you. Looping back to karma being a self fulfilling prophecy, I say that because if you are to judge people with harsh eyes and constantly pick up on others flaws you will eventually do the same to yourself.
Your brain wants you to do what is good for you until it becomes bad for others, for example if you are in business, which I think is one of the closest psychological areas to being in a tribe, in the early stages you need to put yourself above others so you can get to the top and your brains instincts want you to get to the top. Then once you climb the ranks and gain influence over the business your brain switches from thinking of itself to thinking of what is best for the tribe and what will make the tribe thrive and if you go against this your brain will become annoyed and you will begin to pick apart yourself and the decisions you make.
Complexity of the brain:
As we are pack animals when we are in a position of power our brains want us to do what is best for the pack so when you are in a position to help the pack and don't your instinctual brain will not like it. It becomes so complex in a modern society because we are split of into are many different tribes but as we get smarter we also see all of humanity as one big tribe and further than that the earth, natural you protect your home which includes keeping it clean, tidy and in a good condition and now we have evolved to understand that the entire earth is our home we have the natural instincts to protect it.
With all these different thoughts of what our instincts tell us, what our selfishness tells us and what science and exploration tell us our brains really are a big mess of information constantly computing. This is where I think karma comes into play, our brains tell us to do things for ourselves at times but if it will be massively detrimental to multiple other people our brains say don't do that and if you go against your brain you will begin to regret not following it and because our instincts tell us what we have done is wrong they will try to stop us from doing it again.
So if you are doing wrong eventually your brain will have enough and start to sabotage itself to protect the wider tribe and home. This I think is the larger aspect of karma, if you become detrimental enough to your natural home or people your brain will say enough is enough and do all it can to stop you causing more harm, so all the negativity you put out your brain will bring back upon you.
Smaller scale
As a briefly mentioned before if you look at people and start to pick their tiny flaws and always pick apart all the small details of people and generally focus on tiny details you think are bad you will begin to do the same to yourself and pick out all your tiny flaws and every little thing you do that could be annoying, you will also begin to listen more to negative things people have to say about you because you are making your brain negative.