The truth is that every time we give ourselves an excuse to quit, we get better at quitting. But every time we don’t quit, we get better at pushing through. So, both quitting and not quitting can become a habit. And an identity.

Reasons we quit :

1. Not seeing benefits.
2. Fatigue and anticipation of future fatigue
3. Perfectionism (all or nothing thinking)
4. Success would move us out of our comfort zone.

Lab Experiment:
Let's do some reverse engineering. Think back to the last time you quit or gave up on a new hobby, task, job, goal, or whatever.
Once you have it in mind take a deep look at two things:

1. Was this a potentially beneficial activity? If you had continued to do this thing, how would your life look in 2 weeks, 2 months or 2 years from now? — If the answer is “not that different” then choose a different activity.
2. Why did you give up on it? Were you not seeing benefits, were you bored or tired of it, did you feel like you were running out of willpower, were you not able to execute it the way you had imagined, did your perfectionist side creep out, or were you frightened of what your life might look like if you succeeded?

Now, once you have zeroed in on one (or maybe more) of the reasons for why you quit, can you figure out how you might be able to remove some of the roadblocks to make it easier and more likely that you will succeed next time?

Resources: 

Make “no quit” Your New Habit (Brock's Weighless LIfe blog post)

The central governor model of exercise regulation (National Library of Medicine paper)

Which wolf with you Feed story