I have now heard a lot of people talking about they are waiting for bitcoin to drop, so that they can buy bitcoin. But these guys might have said that since 6k$ and are still waiting. What do you tell those people, to try and make them understand that waiting for a drop can cost them huge percentage gains?
I'd like to congratulate those people you've heard from December 2017, wait is truly paid off (If they have truly wait)

nothing to make them understand, seems they do know what they're doing and anticipated this event
TBH I myself couldn't realized until mid Feb that BTC is really going down
It give a way to open door and to understand TA's and trading much more
and Voila, it explains it
I have realized already that I should sell some of my coins last year to book for a profit, I was to greedy not doing it and now I have to wait
to see a good price again. I just feel I did not act on the right timing but I don't feel also that I loss money now because I can still hold for longer than a year.