What is one thing you wish you had known at 21?

I don't really know and I don't really take anytime on thinking about it. But I have a feeling that it may be the most valuable thing will would do in my life.
30 minutes' thinking can really clear up my mind.

Here is the answer of Faisai Khan from Quora.com

Read Quote of Faisal Khan's answer to Entrepreneurship: What is one thing you wish you had known at 21? on Quora