Noob, if he thought that way he would have already sold long ago. He will sell when he can think of a better investment to put that money into.
That's not how it works if you actually want to make money from investing. I'm not saying that "long-term hold" isn't a valid strategy, but it isn't one to apply to highly speculative stocks like bitcoin.
Risk management: A good strategy would be to minimise future risk and to lock in gains already made by selling a portion at either a pre-determined profit level, or once it has fallen a certain level from a peak (tip: you can do both with provisional stop-loss orders!). Managing your risk is the most important thing when investing, and once you have made a paper-profit you are at risk of losing it. So lock it in by selling some. If you still believe in bitcoin, you can buy back in later when you think the price has fallen enough and an upward trend is starting.
Another reason to sell some is that highly speculative stocks should make up a quite small proportion of your portfolio. The exact proportion is up to you, but my point is that if Bitcoin has gone up dramatically, an initially small proportion is now a relatively large proportion of your total portfolio. If something happens to it, you'll be hit hard. So again, de-risk yourself by selling some to bring your portfolio balance back into line.
If you don't care about portfolio balancing then you don't care about risk, and you are just gambling. May as well head off to Vegas.
In general you shouldn't sell something just so that you can buy something else. That's because the best times to sell and buy rarely coincide. Rising tides lift all boats, and rising markets lift all stocks. The time to sell is usually when the markets are up, and the time to buy is usually when they are down. It is therefore good practice to be disciplined with your buying and selling decisions, don't link them directly together because you set yourself up for selling and buying at the wrong times for the wrong reasons.
Might sound funny but when the GFC hit, my first thought wasn't "OMG my stocks have lost all their value!", it was "damn, I don't have enough cash to take advantage of the bargains". If only I'd sold some stuff earlier at "fair value", made some more cash available, I could've made a killing on undervalued stocks. But selling into a depressed market to get money to buy stuff with is crazy. The best times to buy and sell rarely align.