"Decisions Determine Destiny" 
                                                   "The path you take is the decision you make"
What i think decisions determine destiny is that we are the one to make our destiny. We are the ones to choose whether to make the good or bad decisions. Our destiny can only be made because you decide whether you live to see yourself become what you want or you die and never get to make your destiny. The decisions you make are like a game there are always gonna be results whether good or bad. They will always have consequences to what you choose. Like if you chose to save the woman from a falling building the odds of you living are 1 to to 1,000,000 but you would be known a hero due to the choices that you have made but dead. Although if you don't save her you will live with the feeling that tells you that you could have saved her which will cause you to go through depression and even commit suicide because of it . This is all led through the decisions you make which make up what you call Destiny.
EX: An example of this is a game called "Until Dawn". The reason why I choose this game as an example is because the game Until Dawn is only played by the choices you make whether to jump down to the mines or look for help. Or from choosing who to save between your best friend or the the girl you have a crush on.