Which decisions I make today will affect me for my entire life?

The decisions that will affect me for the rest of my life are very important. Like whether I choose to stay in school. Or whether I choose to dropout, which I'm not. Also, what college I attend, and what I plan to do while I am there. The last one is what I plan to do when I graduate. I struggling a little bit with math, but other than that, I am doing okay in school. When I am completely finished with school, I want to have my PhD. I am still deciding on whatever it is going to be, but whatever it is, I know that it will be good for the rest of my life.