something like four days in the year. It's a shockingly low number.
Which is why staying more or less fully invested (less does allow you to have cash to jump in when there is a drop) and just ride things out.
The other thing is that you need to take a truly long term approach. I've been investing since the late 1970s, and over those years I've done quite well. I have not made a killing, mainly because I'm not buying individual stocks any more, which I did back in the first ten years. I have a reasonably balanced portfolio, have an excellent money manager whom I trust.
One thing he did for me was to get me into a couple of annuities a decade or so back. Now I know that people love to trash annuities, but there are some very good ones out there. I have two of them. I started taking the payout from them about a year ago. I'm now 71 years old which is pertinent information. The amount each pays is fixed, and whatever value is lef over when I die will go to my heirs. If I live a really long time, I will have used up all that value, but that's just fine with me. And my heirs are not -- they'd better not be -- sitting around waiting for me to die so they can collect a bunch of money.
Selling off just because you think the market might go down is a poor strategy. For all that people piss and moan about the market under Trump, it is still somewhat above what it was when he took office.
On the other hand, taking profits can be a good thing. If you have a stock or mutual fund that has risen a whole lot, yes, go ahead and sell at least some of it and take that money and do whatever you want. A vacation in Tahiti. Fund a kid's college. Buy a new home. Put it into some other stock or mutual fund. Whatever rocks your boat. But that's very different from trying to time the market.