Some get lucky based on timing, but few seem to be able to do it purposefully.
I have always kept some cash available for investing on dips - never been able to call the big drops, but did over-invest at the bottom a couple of times, like Dec 18, and COVID 20, but it was excruciating to do it. I bought stocks and ETFs.
I screwed up later in 2020 and went cash on about 25% of non taxable accounts, and since then have been easing back in, mainly on specialty ETFs like ARKK ... BUT, to be clear, I should never have sold that 25% to cash.
BTW, I resisted selling when the markets got really hammered a decade earlier ... perhaps because I had no time to overthink it - too busy with life and kids ��?