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Book profits should be based on various factors. Sometimes a token rallies up way before the news event happens. This rally can continue until the end of the events which depends on the importance of those events. There is a saying in the crypto market and that is "Buy the rumors and sell the news". If there is a rumor going on then you should start accumulating that project and book the profit as soon as the news event releases.
When someone understands enough how the market works, then of course they can take advantage of any momentum to generate profits. You don't have to trade every day to make a profit, but you have to be able to do analysis enough so that you can make a profit when trading.
We are all aware that sometimes price movements do not always match our expectations, but good analysis can usually help traders to get commensurate results. The saying you say is true, but there are always different strategies that can also generate profits. Rumors are not always true, but some rumors can come true so there is no harm in taking advantage of such things to gain profits from trading.