One person's loss is another person's profit. The market runs on buy sell right? So if person A buys it and makes the price higher, then if person B sells it, then the price will fall down. That's the same thing that happens with the crypto market. If people keep on buying and make the price higher, there will be people ready to sell. Just like you said, you will get a better value if those people keep on buying. But if you want to profit from it, you will sell for sure. It's not only just you, there are others waiting for that too. So the price will fluctuate and those who buy the green will be in red again. And they can't keep it up for forever.
Take the chance while you can make a profit. Don't get affected by greed. It will only lead to losses.
Crypto currency market is also working with profit and loss like other markets. Some people are selling with a good profit, while some people are exiting the market at a loss, but I think only those who buy at the right time can make profit in the crypto currency market, because a well-timed entry can give anyone good profits. Take chances, but with proper strategy. If you are getting profit, then sell 50% of your assets.
If the price increases further, then you can sell the remaining assets with good profit. If the price falls back, you can buy back at a lower price. Just as one must find the right opportunity to buy, one must always sell at the right time to sell one's assets at a profit. No one has ever seen a perfect bottom and no one has ever seen a perfect top. So always sell your assets not just at a profit but at a reasonable profit.