Enduring Pain - Guidelines for the Heart by Ryuho Okawa 229 -

As you navigate through tumultuous times, your soul shines, and joy increases. It is indeed tough when facing hardships and difficulties, but (omitted) humans grow significantly during this process. (omitted) When you feel like you are being torn apart by anguish, overcoming it gives rise to great confidence.
(From Chapter 2 'Principle of Accumulation')

Continuing to balance study and exercise requires tremendous willpower. (omitted) You must encourage yourself while training, but gradually, a kind of 'power of habit' that could be called the law of inertia begins to work. When you can enjoy it without feeling the effort due to the power of habit, you can say that you have significantly improved.
(From Chapter 3 'Do Not Lose Your Hungry Spirit')