This is one manual I believe in so much: when we do good to people, good things happen to us, and when we do bad things to people, bad things (karma) happen to us. This is so real because I have experienced it many times, and I have seen people experience it too. But sometimes, the time at which we receive the good returns might take a while, and this makes it look like it doesn't always work this way to a lot of people, but it does. If the good we did doesn't come back to us while we are alive, our children will reap the benefits. It's just like that, and it is very natural.
There was a time I went to a barber shop to cut my hair. I got there and met a lot of people in the queue, and because that was my favourite place to cut my hair, I decided to stay and wait. While waiting, a man in his 60s came hurriedly and begged people in the queue to give him a chance to cut his hair because he was in a hurry and he wouldn't be able to wait for his turn. While everyone in the queue refused, I agreed that he should take my slot, and meanwhile, there was just one person before me. When I agreed, the people behind me told me that I would have to wait till they're done with theirs before I cut my hair, and I didn't argue. I did what I did by having empathy. Meanwhile, when the man was done cutting his hair, he gave me triple the amount I would have been charged to cut my hair. I was surprised that night, and I didn't expect that at all. That was a time I did good and got an instant repayment.
Meanwhile, when we do good, we don't usually expect to receive the return in the same format. This is why I don't think I have done any good and haven't received the good returns. Maybe it has come, and I didn't know, or it's yet to happen. I don't even take my acts of doing good to heart. I just be a human being and wait to receive the rewards whenever they come.