As far as fluctuations, selling at the top, etc.
It's like with most stocks. You sell at a certain price, it drops below that price, and you think...GOOD! I did the right thing. Next thing you know it's way above your price and you realize that the market makers simply grabbed your shares cheap and they're laughing at you on the streets.
I've been stock trading for so long that I eventually learned with stocks to just buy and hold, or at most, position trade over the course of days, or weeks. I no longer panic or worry about intraday fluctuations.
With BTC I have been in for the long haul since 2013, with regular, consistent accumulations ever since, and have no reason to sell yet.