One question bothers me a long time and I am not sure if there is anyone that thinks about this before. Let's say you invested $10K in Bitcoin when the price was $20K, and some time later the price pumped to $40K, which means the initial capital is now worth $20K. For some reason, you need cash urgently so you decide to sell the Bitcoin you own for cash. You do it and now you have that $20K on hand.
If you have to sell because of an emergency, you're doing it wrong. An essential principle of personal finance is to have an emergency fund of between 3 and 6 months' worth of cash. That if you live in the USA or a similar industrialized country could very well be the $20k you are talking about. In addition you may have other types of assets that you could borrow on at low interest rates if you don't want to sell the Bitcoin.
For example, at your bank you have $20k in an emergency savings account, $150k in pension plans, and another $50k in stocks or mutual funds, your bank will be happy to give you a loan if a supposed emergency exceeds $20k, but I for example in the last 15 years haven't had an emergency that exceeded 10% of that
So, if you manage your personal finances well you will not be forced to sell, and you can hold the Bitcoin for a couple of cycles at least, to then consider whether to make partial sales.