You can simply set exit and entry goals, and not overthink it; the described strategy implies that we act on emotions, FOMO may kick in, and do you really need that?

For example, you buy $ETH for $3000, the price increases to $4000, but then drops back to $3500. You regret not selling at the peak and feel that you lost $500 in profit. This leads to two potential consequences:
1. If the uptrend has not yet ended: you might take profits early because you are worried about a correction and miss the next growth opportunity.