It depends on the reason you are selling. If you're selling to invest in a more profitable asset, it's actually the opposite... The difficult task is to find something better to invest.
Bitcoin is a safe and profitable investment, I do not see a big risk there. Every year BTC increments are very good, just need to prepare your mental to hold in an uncertain period of two years or 1 year.
Are you sure? I remember in four years ago, in 2013 - 2014 the price of Bitcoin has breakdown bubble growth and falldown -1000% with the highest price. So for me, don't have type investment is safest, always have the risk when investment.