Lao tzu spent years meditating to understand essence of life. In reign of zhao he realized that war would break out and will destroy place where he lived. So he made simplest possible choice and decided to move to another place. He took few of his belongings and set off. On his way to leaving, he met a gatekeeper. Gate keeper recognized him and said, "Where a sage like you is going??"Lao replied, "Somewhere far away from war.."Gatekeeper said, "I would like to know what you have learned from meditating all these years.. I won't let you leave until you share with me.. what you have learned.."Lao tzu wanted to leave. So right there he wrote a whole volume about what he learned and gave it to gate keeper and left. No one ever heard from him again. . 
Here are some life changing teaching of lao tzu: 