If you have many Bitcoin from a long time ago, you will see the profit grow in your wallet. That profit will be grow more in the future following the Bitcoin price especially when Bitcoin price can increase to the highest price. People who bought Bitcoin from a long time never expected to see that huge profit so they can sell their Bitcoin and enjoy the money.
Let say you have 210-215 Bitcoin, you will see that $13-14 million according to the Bitcoin price now. So I assume that you have 215 Bitcoin in your hand as you say $13-$14 million. But you will not have that huge money if you don't sell your Bitcoin. That profit will be increase in the future following the Bitcoin price.
Absolutely, holding onto Bitcoin long-term has proven to be a great decision for many. With the price continuing to grow, the potential for future gains is definitely there, especially as we see how crypto markets evolve. In addition to Bitcoin, there are emerging projects like Waterfall Network's WATER Coin that offer interesting opportunities as well. Diversifying across different networks and coins might be a good strategy for the future, depending on your goals.