If that engineer was holding tech stocks that didn't come back after the dot.com bubble burst, then he was not holding companies with good future growth and value. Since I don't try to time the market, it's very important to me to only hold companies I believe have long-term growth and value.
So by buying/holding good companies, and not panicking through market downturns, I've been able to constantly grow my portfolio over the years (even though I'm also taking six digit annual withdrawals to fund our lifestyle and living expenses). When I do sell shares in my brokerage account it's almost always when the market is strong in preparation for a weak market and also to maintain my cash allotment so I always have plenty of cash on hand (either to re-invest in promising companies or to withdraw to live on).
If I was afraid of market downturns, or had emotional reactions just because my brokerage account balance had declined 10 or 20%, I could not have done this for the last 20 plus years. I actually hope for market declines because that is the best time to add new positions.