Being persistent at your goal requires discipline. It's what you should do to move one step forward towards your end goal. It's difficult and painful.
However, if you don't carry out your work and be persistent at it, you'll regret it. You'll regret that you weren't consistent at your goal. Because if you were, you'd be closer to success. Of course, success depends on how you define it.
At the end, it comes down to this: either pain of regret or pain of discipline.
For example, you might have a goal to not eat junk foods to stay healthy and fit. Doing so requires lots of willpower and determination. It's easy to enter the vicious cycle of resolving to not eat junk food, eating junk food and again, resolving to not eat junk food. It just keeps moving in cycle.
If you eat junk food, you'll regret it later. While you see junk food, you'll just think that you're in pain of discipline, not being able to eat what you desire. You try to make it easy for yourself and eat it, not realizing that pain of regret will follow.
We only realize that there is pain of discipline, but fail to realize that pain of regret will follow if we lose out on pain of discipline.
We humans try to set ourselves free from the factor that's causing us pain. Here in the example of junk food, that pain comes from discipline of resisting to eat junk foods. So we try and remove that pain by eating junk food, only to find pain of regret following us.
If we're aware of pain of regret, it will at least be easier for us to not eat junk food, realizing that we won't be free of pain.
We need to embrace pain, because that's a part of self improvement journey.
So, next time when you set out a self improvement goal, realize that you have two choices during your journey: pain of regret or pain of discipline.