I've told people to buy at $3,800, $5,900, and $14,000 and got shouted down each time. All of these were after major crashes, so of course the price was about to bounce back.
Even if you know when the music hasn't stopped yet, it's very hard to get anyone to listen.
For what is worth, I also thought that ~5500 dip in mid november was a good time as well. I wish I had money in the exchange that weekend because it quickly recovered days afterward.
The recent dip was scarier though and time will tell whether we are still on the rise or just a temporary recovery.
It's easy to see in retrospect that the beginning of bitcoin would've been a good place to throw in some meaningless quantities of cash, but I think once you divide by the number of small, potential investments you could make that wouldn't have made you money, and subtract the amount of time commitment to keep track of those investments, the outcome is less appealing.
(Obviously, some people knew it was about explode, but I'm looking at everything you hear your kid, or a co-worker giving you hot tips about, which was the boat I was in and it sounds like this kid's dad was in).
Even if you know when the music hasn't stopped yet, it's very hard to get anyone to listen.