To me, being successful means...
Feeling fulfilled in life and doing something you enjoy, life is too short to be unhappy.

My definition of success has changed over time. 
Yes, in high school I didn't try at all I barely graduated high school with a 2.0 GPA. It wasn't until I decided that I wanted to take school seriously that I excelled. I went to community college which I thought was easier then [high school] then pursued my bachelors degree and I am currently in graduate school and I should be graduating with honors next year.