Maturity is patience; it is knowing how to postpone immediate pleasure in favor of long-term benefit.

This phrase connects us with The Principle of Delayed Gratification.
Psychologically popularized by the famous "Stanford Marshmallow Experiment," this concept is the single most accurate predictor of success in life. It defines maturity not by age, but by the ability of the executive brain (logic/planning) to override the lizard brain (impulse/desire).
1. The War Between "Now" and "Later"
The Child/Animal Mind: Wants the reward instantly. It cannot conceptualize a future version of itself. "I want the candy now."
The Mature Mind: Understands that the "future self" is real and needs to be taken care of. It is the ability to empathize with who you will be in 10 years. If you eat the seed corn today because you are hungry, you will starve next winter.
2. The Compound Interest of Suffering
"Postpone immediate pleasure."
Every significant achievement (a degree, a fit body, financial wealth) requires a "down payment" of discomfort.
You must pay the price of discipline before you get the product of success.
Immature people try to buy on credit (pleasure now, pay later with interest). Mature people invest (pain now, dividend later).
3. Low Time Preference
In economics, this is called having a "low time preference."
Societies and individuals who can wait (save money, build infrastructure, study) accumulate capital and power.
Those with "high time preference" (spend immediately, skip the workout, react emotionally) are perpetually trapped in the present moment, unable to build anything that lasts.
Golden Rule: Never trade what you want most for what you want now. The ability to say "no" to yourself is the ultimate power. If you can conquer your own impulses, you can conquer almost any external obstacle.