As of June, 2017, the stock market indexes are essentially at all-time highs which have increased the net worth of individuals considerably from the stock market lows of 2008, but like anything, nothing rises forever, and fundamentally stock prices have to have some sort of tangible relationship to the underlying intrinsic worth of the stock to begin with. When times are good, a lot of this is somewhat ignored, for markets in America, are quite liquid, consistently and reliably open, and with both buyers and sellers in abundance, the market is said to be efficient.
Another prospective, though, would indicate that markets are not quite as quiescent, reliable, and consistent as one might imagine them to be, in fact, to ignore this, may entail rather dire financial consequences. For instance, present day trading in stocks, are typically not conducted by individuals bargaining back and forth, as was the case, back when stocks exchanges were first conceived of, as the vast majority of trades are now automated, using advanced algorithms to take advantage of inconsistencies in pricing, trading patterns, and optimization, for such automation obviously carries the seeds of its own potential destruction, for "black swan" events do occur, and the robustness of automated trading strategies when panic is in the air is the true acid test of how failsafe that they really are.
Additionally, as in all investments, the leveraged of the money being utilized, especially the higher the amount of leverage drawn upon, creates a higher degree of volatility for the greater amounts of money so borrowed, which has to, at some point, be paid back, and those loaning such, have conditions that must be met, in which, within these terms and conditions, leverage, which institutions and individuals often take for granted, and even build their castles upon, cannot be guaranteed continual access to, as well as the cost of that leverage can rise substantially, especially in the moments of time when most needed.
Further to the point, the more leverage there is, the more potential panic there will be, as investors, automated or not, unwind voluntarily or involuntarily their stock portfolios, causing a cascade of selling pressure upon investors, so that investments that looked absolutely secured the evening before, have lost value in double-digits in one day, or even have collapsed completely as does happens occasionally to individual stocks, especially those that have questionable intrinsic value to begin with.
The difference between leveraged money and money that is actually yours, lock, stock, and barrel, is the difference between night and day, in which, leveraged money because it is leveraged, loves the market when times are good, and when times are bad, has as its overriding objective, a flight to safety, in which, the first one out of a sinking ship, has first access to the safety boats so attached. This means when there are nothing but sellers, prices fall, and they will fall precipitously, and while pundits admonish us all of the time that the best time to buy is when there is "blood in the streets", panics have a way of feeding upon themselves, because most people have an abiding interest in at least retaining a portion of what they once had, rather than the ignominy of losing it all.
The bottom line is that borrowed money and leveraged used in investments, will ultimately create more volatility and far less stability, especially since so many believe in their infallibility as well as their impeccable timing, till a monstrous panic ensues, whereupon greed takes a back seat to pure unmitigated fear.