Set yourself a threshold amount that you are okay with a 100% loss on, and a periodic schedule based on your risk-appetite. At each interval if you are above your threshold you sell your excess holdings and if you are below you sit tight.

Alternatively you can set yourself a price threshold. For example, sell half your holdings every time the price doubles. Essentially this acts as a log function on your gains in exchange for lowering risk.

There's a ton of room for fine tuning a set of rules to manage risk, as long as you are willing to stick to them.

Personally I would sell what I'd call the "FOMO holding" once it's worth a "life changing" amount of money. So if I held 100 Bitcoin as such a fund, that might well have been years ago, but then I'd also be retired and not care. The sister comment here is more nuanced and surely a better answer, though.