Buddhism teaches karma.

Buddhism teaches karma. 
Karma means "imprint". 

In other words, everything you do, say, think and feel sets imprints inside yourself. Every second you are alive, you are either creating new imprints in yourself or you are strengthening existing imprints made previously by you. 
In turn, you are drawn to situations that match your imprints. You draw situations to you that match your imprints. This is how the world responds to us .. us as we have made ourselves. There is no "higher power" to karma. 

Coincidence? No .. it is the causes and consequences that we have created for ourselves .. our inner imprints. 
Is there a reason? Like a "meaning" or "lesson"? No. It is just "is". 

Sort of like gravity. If you step off a cliff, you fall. When you step off the cliff, you set in motion the causes and conditions to fall. There is no coincidence to this, no meaning, no lesson. It's just the way things happen. 

So if you feel angry and you feed your anger by dwelling on it, even more by acting on it .. over time you become a very angry person. At least, there are strong imprints in your brain, strong pathways for "anger" to run along. 
In turn, those people who are kind and laid-back will become uneasy around you (they will sense your anger, as their unconscious minds will pick up on your subtle subliminal signals of impatience and anger) .. and they will avoid you. Instead, you will attract other angry people, and your experiences with these people will be different from the experiences you would have had with the kind, laid-back people. 
This is the way karma works. You make it yourself, and you can change what imprints you make within yourself 
too.

Read my other articles here