" Decisions Determine Destiny" 

This quote means that if you make a decision you need to determine that decision so it can be your destiny and you will achieve your destiny/goal.

For example if you were to make a decision of doing all your work and turning it in on time and getting good grades you need to stay determined on that decision and make it your destiny. you would need to stay focused on that decision to achieve your decision on turning in your work and getting good grades.