Since the replies have focused on the "fear of investing/ also of not investing" issue, you might want to consider looking at the whole process from another angle: for me this whole frugality, conscious spending, whatever approach is more about taking charge of my own choices. The most important benefit, in my own mind, is environmental. Over consumption = needless waste of resources and pointless contribution to our climate crisis. So whatever happens to your $ investments, this "investment" is a way bigger deal, long-term. And long term means 30-100 years, here. Your kid's lives, and their kids' lives.
Next, I find jumping off the hedonic treadmill totally rewarding. Slow down, calm down, enjoy your real life. Not your consumer life.
When you do these things--limit consumption to a reasonable level of luxury, stop mindlessly consuming--you will find that, IF you are moderately well paid, the $$ just starts piling up by itself. You could keep the $$ in a savings account if you felt like it. Yes, this would delay your total FIRE date, but it would still give you massive freedom and, as they call it, FU money. Even if you just make super -safe interest only investments, same thing. First, take control. You've done that. Then, decide what to do with the mounting surplus. No panic.
So it's all a question of degree. Make the kinds of changes in your daily habits discussed here, and you simply cannot lose, whatever comes. (After that, yes, there's demonstrated benefit to taking some risk, see the Trinity study, etc etc.--but that's another choice you get to make when you take charge of your own habits.)
