Also, Roz (and everybody knows this, but stuff that "everybody knows" often bears repeating) never invest more than you can afford to lose. Because you might.

And jumping in because the timing is perfect is great... or not. I jumped into tech stocks after the market collapsed in the Dot Com boom aftermath, because tech! It will always be with us! Have to go back up, yes?

It turned out I did not fully understand what a “market collapse” actually consisted of. I actually jumped in after a “market correction,” which apparently means “OMG I can’t believe how much the market tanked!” until there is a REAL market collapse, at which point it becomes a minor inflection before the sheer cliff of a graph showing market prices. Twelve years later, when I sold it off to help pay off our mortgage, the stock had regained enough to where I had to pay capital gains. About $20 worth, if I recall correctly. 😐

tl;dr: My advice to people who ask me for investing advice is to not listen to me for investing advice. (Also applies to relationship advice and auto purchases.)