Selling your bitcoin in order to invest in something else to me, is not advisable, considering the general situation, especially the coming of the bitcoin halving. The price of bitcoin will rise again and possibly go above $69000 and more, so there is hope of making good profit at the end of the day. Unless if you need fund for very important and beneficial project, then you can sell a little reasonable and suitable amount, if not, l suggest you still hold on.
the best thing that he need to do is holding it until the next bullish market trend, that's was good advice. I personally will try not sell any of my btc for anything until it's price reach the peak at bull run. I think it will be better for him to make a plan before investing, maybe it will be good if he divide his fund into some part so he will not touch his investment fund for btc so he will not sell his btc in lower price.
A bitcoiner must have full knowledge about this because when he invests he must wait for a long time. There are long-timers who tend to rush too much when the Bitcoin market turns bearish, but must be patient. However, a person must be aware that the Bitcoin market is always on the ups and downs and there are volatility in the market which can leave him disappointed. So before investing, he should be clear about all these issues.If the market starts to fluctuate, then he should not be disappointed, but he should be patient until the market increases. And it must be followed by an investor not to sell his bitcoins when the market goes down, not to sell until a bull market is seen.