In what ways does hard work make you feel fulfilled?

I have always been taught work smarter, not harder so and everything that I have done I have always found ways to optimize my productivity with out, overdoing it on my body since I love working with children, the goal is to not over, lift them or strain myself in the process of caring for them. This way I am teaching them effort. Oh, responsibility for their bodies and their brains without hurting themselves, and using their smarts more than their ability to use their muscles your brain is the most powerful muscle in your body and using that is the greatest thing I believe you can use to accomplish things in life, along with common sense.