nothing can go up forever. I'd say it is more reasonable to take profit if the chart looks parabolic and the angle gets close to 90. It is easier to take profit from an altcoin than bitcoin since altcoins' price are more derived from the news. Nevertheless you should be aware that there are no perfect trades and you will never get the best out of a trade. Sometimes it is better to go out late than early and sometimes vice versa.
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