I would say it all depends on one's knowledge of the market as a greater factor rather than the environment when you start (with uneducated investors definitely impacted by when they start out).
I started investing in 1992 at the ripe young age of 16 with a pool of my (25% share) and my older siblings money. Began by buying treasuries at the auction, then flipping them for some fractions. In a declining rate environment, it's easy money. Then began salivating at how much more I could make by simply flipping stocks for just a mere 1/2 point! Tried that and also was a bottom feeder by looking for stocks making 52 week lows. I made a few ok decisions, but made more blunders (like listening to my majority share brother who said "never sell a stock at a loss! Just hold it!"
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Between 92 and 99, I made a few very bad investments - I went from starting out to -40%, back to roughly break even, back down -50%, back to break even, then down -30%, then back to break even, as I learned to day trade quite a few stocks for small 1/4, 1/2 or 1 point gains and cut and run and recover the portfolio. So, I was somewhat of a risk taker (by necessity to try and recover the portfolio).
So after 7 years, it was still at break even, despite being in a great bull market.
At that point, getting ready to graduate college, I began to be tempted to invest in internet stocks, after staying away from the high flyers with PEs of 10,573 (if they were positive at all). In the end, I said "to hell with stocks, I'm going for the easy 7% (post-tax) in muni CEFs and REITs". Turned out to be an excellent, well-timed choice (FINALLY!).
Gradually grew the portfolio, but still was heavily weighted in REITs/preferred bonds/muni CEFs for the relative safety - and seeing my grandparents having a very comfortable retirement with their 100% Treasury Bond portfolio didn't sway me away from the 'steady Eddie' 7% annual returns of my holdings.
However, stumbled onto this forum circa 2005, and began to learn about the benefits of stock holdings to beat inflation long-term. Finally began to be more aggressive and began moving big chunks to international holdings. Currently about 30% foreign stocks, 20% US stocks (with some international exposure), a big chunk (15%?) in oil/mostly pipeline MLPs (debating on whether to liquidate them given their current yields), and the rest in savings bonds and preferred stocks.
To sum it up - in the beginning, even though I've seen the markets around me rising, and I knew the market overall was a good place to be, I thought I could do better than some mutual fund manager (perhaps there was a little 'control freak' issue going on as well, mixed in with my teenage hormones). I then ended up becoming (what I saw as) far more risk-averse because of my specific experiences in investing, rather than the general market. And then full-circle to reach my current outlook.
For me, if the 90s had been a bear market, I simply would have still done my research to find investment opportunities and stayed the course, rather than recoil and be controlled by knee-jerk reactions.
Of course, for the average Joe and Jane who invest in many mutual funds that do worse than the market, a bear market means Joe and Jane's funds will do even worse...definitely making them even more risk averse when they rush to sell on the way down/at the bottom, and take far longer to recover than if they had just stayed the course like an educated investor would do.