Not selling you coins ever is the worst thing to do, if you are earning profits you should sell it and again wait for the price to fall down, do not hold your coins too long.
sometimes after you sell your bitcoin to take profit, the bitcoin price keep rising to the moon, and the fail not reached your sell price, better to sell some and keep holding for future don't sell alll of your bitcoin
Correct, never sell all your coins, keep some in buffer stock as we don't know what would be the price of bitcoin in future, so its always better to keep some coins safe in wallet.
if i can predict or analisys when the price down(after reading some analisys from newsbtc), i prefered to sell all of my bitcoin then iam buy back at lower price , after price rising again, i sell only the profit and keep hold it
That's impossible to do, are you an astrologer who can judge the perfect price or perfect time to buy or sell bitcoins, if everyone would be able to do it then everyone would get super rich with bitcoins.