Well the way that usually works for most traders is they buy at say 37K, it goes to 39K and then starts dropping. The trader dumps at about 37.5K and notices that it drops below his 37K buy, and then as he's slapping himself on the back, it rallies back to 38, 39, 40K and beyond. That's a best case scenario for most traders.
Others will end up losing money as it dips below their purchase price, or, if a little more disciplined, holding only until it's just a little higher than the purchase price and letting go for peanuts, only to watch it rally back much higher.
In sum, unless you really are a good (and lucky) trader, it's just better to get in and HODL with something as volatile as BTC. Once you're stratospherically in the green, these fluctuations don't mean so much.