I/DW are both retired. We started our "investment journey" last century
in '82, after our respective pensions (different companies) were eliminated.
Our first "major glitch" was of course in 1987 a few major, and many minor ones to follow.
In 1987, I was going to night school for my BS degree (at the ancient age of 39, since I received my physical/draft notice in my "early years"). At the time, I had this "old phart" as an instructor who did invest, and gave me the simple (but valuable) advice that markets will always go up/down over time, for various reasons.
Assuming I had a job which covered my day to day expenses in the present day, what did I really lose? The market could lose most of it's value, but I still would have a place to live and food to eat. That's better than most of the world's population at that (and this) time.
I didn't do anything in '87 nor 2000-02. In fact, during the tech meltdown I/DW did extremely well. While most folks were investing heavily in tech during the mid/late 90's, DW/me took the opposite approach and paid down all our debts, including our home - which we were making payments that allowed us to pay off our 30-year note in just over 5.5 years, in late 1999.
What did we do then? Simply took the mortgage (actually note - mortgage is the incorrect term), along with the "extra" we were paying, and put it into the equity market. Even though it was "meltdown time", we did not care; heck, we had a roof over our head, enough to eat, and we were both employeed.
That was a period that allowed us to amass significant retirement assets, since we bought cheap in those years.
In early/mid-2000, we decided on a retirement scheme to leave our respective employment at the age of 59. Not really early according to a lot of folks on this forum, but earlier than the SS FRA age of 66 that we had planned on many, many years ago.
Around the age of 55, we started building up our retirement cash reserves, since we were going to be retiring without a pension (me; DW has two small one's, starting next year at age 65), along with our planned SS draw dates of 66 (FRA - DW) and age 70 for me (primarily for the benefit of my DW, assuming I'll die first, along with 50% of DW's SS from my age 66-69).
Even though I retired in early 2007 (DW did not follow me till a few months ago - she was not "emotionally ready"), the downturn of 2008 meant little to me/us. I had the cash (and so did DW - we established it that she could retire on and day she chose) and had been through enough downturns to remember that markets go up, and they go down. There is nothing the same under the sun, and when some pundit states "this time, it's different", it really isn't. It's just that they have not lived though a similar time in their own life.
We add to our retirement cash accounts when things are up (as we have for example, last spring and this spring) and just sit tight when profits are lacking. We have yet to sell (nor intend to) on a down cycle, primarily due to our extensive cash holdings, along with future retirement income that will start in a year with additional funding sources coming "on-line" over the next five years.
Anyway, we learned that flux in the market will always be there. You need to understand, and accept that fact - even though it's not easy, especially for the first few times. That's our story, and hopefully answers your question, based upon our reality.