This is why I love long term investment. I feel like there is nothing that I need to check aside from having a good future and a great fundamental and not being a scam. Like for example if you build a basket with bitcoin, litecoin, ethereum, ada, bnb, and coins like that then you are going to make a profit in 10 years.
I am not sure if ALL of them will be high, maybe one or two will go down and not liked anymore and will not profit you and just crash and be gone. However, the overall will be profit for sure, that is what I am sure about. Even if you buy simply just bitcoin, you will be able to make a big profit in 10 years. This is why long term investment is easier. If you want to do short term, you will need to educate yourself a lot more than anything else and it would be very difficult, not impossible but very difficult to do.
Having these kind of coin in your basket like bitcoin, ethereum, ada, bnb, sol, and xrp you would not going to feel threatened to hodl it for a long time investment. I mean that you know in yourself that these coins are worth it to hold and valuable even in the long run because it's use cases are usable even in the following years. Answering the question of OP of when you know a time to sell my answer is depend on your choice, it's depend if the market price of your token is enough for you to sell and if you are going to earn from it the. It is better but if you know you will not going to profit from it the. Why would you sell right.