Pertaining to the FB buy a month ago, I think the instructive point here is that by buying on the dip, he was able to lock in a price that hadn't been that low since July 17, 2017. That means he was able to lock in a price that hasn't been that low in almost a year!
And if there was any question, it's gone up a hefty bit since then.
Clearly, a buy on the dip swing trade that worked.
Of course, if we are on the cusp of a calamitous 60% drop, he would either need to sell and take some profits or be willing to ride it out. But that is a big "if".
For what it's worth, i started buying Netflix a year or two ago on just such a dip, when i think it was trading for about $89. It turned around within a few dollars of that and started back on a tear upwards. I swallowed hard on the way up and bought a few more times, each time realizing it was half crazy to be buying at those valuations and prices. But damn if it hasn't paid off far beyond my expectations.