Markets haven't been around for decades, they've been around for centuries
Contrary to popular belief, financial instrument and commodities markets aren't gambling casinos. And the major stock markets overall are one of the better ways to accumulate wealth. You simply need to follow some basic and well-published rules and determine what sort of goals you have. Based on your goals, you adopt a strategy. Your best chances for success are to be consistent in following that strategy, although goals (and hence strategy) may change throughout life.
Perhaps the most basic rule of them all is that the bigger the payout, the bigger the chance that you'll lose some or all of your investment. So if you expect to retire in comfort, don't grab at every get-rich-quick scheme that comes along. It's a good way to make a small fortune - assuming you started with a large fortune.
Investing is very much a bootstrapping process, Which means that if you can't afford a pair of boots to begin with, look elsewhere. If you have to tap your investments every time you need new soles, you'll lose. You do have to have money to make money and you need to be able to make your decisions on your own schedule, not someone else's. The people who got wiped out in the Crash of 1928 were not the ones who kept their investments, they're the ones who sold. In many cases, they had no choice but to sell, since conditions at the time led too much buying on margin and banks who had a vested interest in being stock brokers. The long-term holders saw their investments dip, then slowly return to (and mostly0) exceed) pre-crash values. Some companies failed, but the AT&T's, General Motors, and so forth didn't. The truly wealthy had diversified portfolios so a few failures were a mere annoyance. The day-traders and hot-tip investors ended up in the bread lines.
Incidentally, I once had over 1000 shares of a popular and now-defunct airline named Air Florida. Lost every penny. On the other hand, I bought Cisco, held onto it for 10-15 years and sold it to pay off the mortgage on my house. I also bought Red Hat not long after it went public
One of the biggest mistakes you can make is to buy into fads. Markets stampede. Once something like BitCoin gains general public notice, everyone rushes in, pushes valuations to absurd levels, the realists cash out and the accelerating sales cause prices to crash. Assuming that the market in question doesn't completely collapse, that's when the more cautious (and successful) investors like Warren Buffet move in, buy up and wait for prices to recover.
Don't try to "time" the market. It's enough to recognize trends. I sold Cisco when it had stopped growing and lost its early fire. I don't think I ever owned Microsoft or IBM directly (since I also invest via funds, what they do is up to them).