There's always going to be that day, most likely multiple days where you sit back and think yourself what am I doing with my life. You'll remember all the friends you've lost, the mistakes you've made, the fun you've had. 

So live your life for those days. Live your life so that when you look back at it you can say you're doing great things with your life. So you can say you're proud of who you are. So you can say you've actually lived.