The logic in a bull market is quite simple: a decline is to bounce back more vigorously, just like a rubber ball that is smashed to the ground; its rebound height depends on the force of the impact. Moreover, in a bull market, declines always have a limit. Once that line is crossed, the market's elastic mechanism will pull it back immediately; this is called a rebound, and it's a law, not a suggestion.
As for a bear market? Sorry, the ball has lost air. Each rebound is a bit shorter than the last, and over time, even trying to jump becomes difficult. So in a bull market, don't waste time fiddling with short positions every day to guard against declines, thinking 'to remain still is to counteract all movements.'
Being in cash every day is the safest, but isn't the point of coming to the market to engage in activities? Even flying has the risk of a crash, so it’s better to mess around on the ground where you can at least enjoy the scenery.