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for a coin is relative or depends on our thinking when to sell. but I personally think we can make a sale when a coin has increased and we can see the potential of the coin, if the coin seems feasible for the long term we can sell 50% and 50% can hold. but if the coin's potential is not good maybe we can sell and shift the profit to another coin with more potential
The exact way you are doing is indeed, we have to anticipate what we will do from what we have, because all analysis is needed which is also very important before doing what we are going to do, because it is possible to analyze the possibility of mistakes going on.
The action to see which coin we have has the potential or not is to follow the trend that the coin is doing, if it has the potential for the future I better agree to remain hold. but if in doubt will divide it in half and will point it to another potential coin so that if it happens We don't all experience losses because there are backups from other coins. Observation is certainly very important if we believe like you said that the coin is not good, it is indeed a good idea to sell immediately.