Affect is generally used to show influence:
A stone thrown at a moving car affects its progress, safety, stability, predictability, etc.
Effect is generally used to show the result:
A stone thrown at a moving car has the effect of collision, injury, death, lack of progress, etc.
This is one of the most frequently asked questions in grammar. I have to stop and think it through each time and sometimes opt for another word.
Depending on your meaning, you could use either one, do you mean "major events that influence your life" or do you mean "major events that resulted in your life"? I suspect that the meaning was the first one, and the most appropriate choice would be 'affect.'