Never sell is the most bullshit thing I heard from crypto people because most of them that spouting that nonsense are those who just want quick profit and they are using that word for shilling purposes. We are all buying Bitcoin to invest and earn in the future so no one in the right mind who will not sell there holdings if they already have a good profit. They should just throwaway there private key if they really want to not sell.

The best way to do is to read the trend in longer time frame. Buy when there’s an obvious bear trend in longer time frame and vice versa. Don’t trade using short time frame because you will be just confused and panic to the price swings of Bitcoin.
The way I understand it when someone declares that they will never sell their bitcoins, it's not that they will keep their bitcoins until they die, they will sell when their profit target is reached or they want to assure people that they have absolute faith in bitcoin, no matter how much bitcoin falls they will never sell it. Many people hold bitcoins from 2013-2015 and so far they haven't sold bitcoins when you ask them during this bear season they will say "never sell".
Those who really understand and see the value of bitcoin have no reason to sell their bitcoins too soon or get too low a profit to sell.