For those selling on the way up, I would also consider selling smaller amounts, and never going 100% fiat (which means never going completely out of BTC), even if there might be some who will choose to sell large amounts of their BTC on the way up.
My own personal strategy is to sell ONLY a small percent for each time that the BTC price goes up (so I am selling even less than .5% for every 10% that the BTC price goes up.. .. even though there are some folks who have recommended selling 10% for every 100% that the BTC price goes up, such as in:
Rpietila's (Risto) 2013 Thread entitled:
(SSS) - A Sane and Simple bitcoin Savings plan Exactly it is not nice to sell all the BTC and empty the coins in your BTC wallet and as that you are not a Bitcoin holder but a Fiat holder on Millionaire or Billionaire. Then later the person would be struggling to buy Bitcoin again and start from the beginning again. Instead as JayJuanGee said, selling a unit to solve the immediate problem is the best way to be a good holder of Bitcoin. Because there are some time that you might need BTC to solve issues online and if you don't have Bitcoin at that time, you would still buy again, to the transaction so it is better you sell small and keep the rest for future use.