1. You will never know if you can go past your limitations, if you don't push yourself.

 2. You will experience the regret of not completing what you started.

 3. You would have put in all of your hard work, time, and effort with no final product or outcome.

 4. You will create a pattern of failure for yourself.  When things get too hard, you will quit. It will become a habit which will create your norm.

 5. You have people depending on you.  It doesn't matter if you what you have started is work related or personal.  You have told someone about it.  Finish, you never know if your completion will inspire someones beginning.