I'm with SouthSamurai and Aella here.
Everything has a reason, in that everything in the present was caused by something in the past. But there isn't some overlord with a plan. Also, putting out positive thoughts to cause positive things to happen to you is partially bullshit, but partially true.
Basically, half the thing that keeps people at their current level is either a lack of desire to go higher, or a lack of belief that you can get higher. Circumstances are the other half, but circumstances can be overcome if you have both the belief that you can do so and the will to do so. Also, you get in the habit of seeing the positive, well, it is everywhere, and everything seems better. Both the positive and the negative are everywhere, and you can choose which perception you pay attention to. It takes a long time to break the old habit and form the new one though.
Somewhat related: control over your emotions.
I believe you don't have much control over your initial reaction. The only way to change that is intensive training that lasts for a full year for every two years that you've been the way you are. However, you can easily train yourself not to give away what that initial reaction is, and train yourself to almost instantly replace it with the one that you want. So in that way, you do control your emotions.
You can choose who you love. But once you give your heart to someone, it's awfully hard to take it back. Once you've chosen to care about someone, you're going to always care about them. If you can't bear to love them anymore, the only other option is to hate them. You can't choose who you're attracted to in the immediate. But you can purposely grow attracted to someone.
All these are things I think about a lot, and I put them all in the same category.