Think of karma like a vector, there is a direction and there is a speed. Everything that you ever do, it is going in some direction. Every time you do something, you are going in that direction. If you always go the same way, you end up very far in that direction and it becomes more permanent. And in your next life, you will also have a tendency to keep going in that same direction.
This is for everything. Good things, and bad things, and neutral things. For example, drinking alcohol is going in the direction of alcohol. It may be relatively safe at first if it is only a small amount, but every time you do it you are going in that direction. Eventually, when the person has gone far enough in that direction, an addiction would have a higher chance of forming and they may become an alcoholic. This would also make it more likely for them to also be an alcoholic in their next life time.
But it also works for good things. If you are always practicing a certain skill or talent, you are going in the direction of making that skill stronger. Eventually, when you have gone very far in that direction, you have built up a very strong talent. Examples of this can be being a musician or an athlete, or anything else that requires a very large amount of skill and practice. Then in your next life time, this same skill will be easier for you than it would be for other people, because in your soul you have already done much of the work. This is why, for example, there are some very young children like 8 years old who can play piano at the highest level, and can perfectly play complicated songs like they are in an orchestra. They have the highest level of talent. This is because they surely have practiced that piano every day for multiple different life times in a row. They have practiced for hundreds of years in past lives, and this practice stays in their soul. So in this life, they have remembered and they have kept that level of skill. And they got back up to that highest level of skill after only practicing for a couple years at a young age.
This is also for personality. If you have a certain personality trait, and this is a big part of who you are, then you are going far in this direction. In next lives, you will be born with this same personality trait, and you will continue having this kind of personality. There may be small changes, if you choose to practice other different personality traits than you will go some amount towards those other traits. But you will mostly stay in whatever way you have spent the most time being.
Somebody who is always very nice and caring, they will always be this way. Someone who is always mean and hateful, they will always be that way. But a nice person can become mean if they spend enough time practicing being mean. And a hateful person can become nice and caring, if they spend enough time practicing being a nicer person.
Anything that you do every day, that is the direction you are going. If you always go the same direction, you will eventually become so far in that direction that it will become permanent and it will become very hard to ever change it. An example of bad karma would be somebody who has addictions. If someone has an entire lifetime where they are addicted to drugs, it will be very high chance of them being addicted to drugs in the next life time. And this will be a very strong force that is much harder to act against, because this force has been building up for a long time. If they spend another entire lifetime of being addicted to drugs, then it is basically permanent. The force keeps building stronger all the time, and after enough lifetimes of that force, it would be very difficult to go against it.
