I don't know what it is, but I've always felt people get emotional about "significant numbers".
Not significant as meaning large numbers, but more like specific points.
For example, why does $19.95 feel so much better than $20 to people?
It's all mental/emotional. You're really not saving that much.
Take that thought into trading now.
If a coin hits $41.23 I really don't care much, but if it's close to hitting a rounded out $50 or $100...it feels different.
It's like a magical barrier IMO that people get in their heads that oh it hit this magic number I feel like it's too high I should take some profits off the table.
I know that might sound super stupid and I have ZERO data to back it up at the moment, but I feel like that's a weird thing for people.
In other words, I not only think people pulled out of bitcoin because it was an ATH, but because it got close to hitting the magical "5k" number.
~nX