You are confusing the whole trade with your friends trade. Just because they made best sell of their life doesn't mean that it will repeat in your life as well. I mean come on brother the best time to sell starts right from the time when you start getting the profits. If you have bought the coin at $9500 then whenever the prices are above this value then that is profit for you and off course the best time to sell everything.
But on the bright side its your decision on how much profits to make. If you want more then have patience and let the bitcoin go up and up.