True freedom is impossible without a mind made free by discipline.

Mortimer J. Adler

Skill is only developed by hours and hours of work.

Usain Bolt

A lot of people are afraid to tell the truth, to say no. That's where toughness comes into play. Toughness is not being a bully. It's having backbone.

Robert Kiyosaki

There is nothing so disobedient as an undisciplined mind, and there is nothing so obedient as a disciplined mind.

Buddha

Self-discipline begins with the mastery of your thoughts. If you don't control what you think, you can't control what you do. Simply, self-discipline enables you to think first and act afterward.

Napoleon Hill

Don't do any task in order to get it over with. Resolve to do each job in a relaxed way, with all your attention. Enjoy and be one with your work.

Thich Nhat Hanh