Who cares if the investment doesn't maximize potential profit? If someone invests $50 and gets $100 in return, that's great. If someone else invests $50 and gets $99.42 in return, that's great too, and who cares if someone made more 'profit' from buying and holding an imaginary financial instrument? The point is: buy "lower", sell "higher" is close enough to buy at the lowest point and sell at the highest point. But other factors come into play on why someone would sell at any time. Theoretically, ceteris paribus mutatis mutandis, if you invest in some company that happens to survive a thousand years into the future and has an annual average ROR of 7%, you should never sell it, even after your death if you want to maximize profit...buy low-ish, sell high-ish as convenient and with common sense. Theoretical perfectly maximized trades should not be the concern of the investor. Count dollars instead of pennies.

The problem you refer to is formally known as "Risk" aka Risk Capital.

The trick is, you don't invest during the downturn, hence all the cash hoarding.

You invest after it bottoms out for a while. Macro economies do not recover like a rocket, the window to invest is very large, so large that if you only recognized the bottoming out a couple years later, you still haven't missed the opportunity.

That is a really interesting point. So I've never invested in stocks before (preferring to invest in my own business) but have decided to diversify and am only seeking returns in a 5-15 year bracket (but want to minimize 1-5 year downside so it could potentially work as an extra emergency fund too).

I had assumed being 20%+ off of the highs, it'd be a good idea to start getting involved now, but.. maybe I should wait until a clear "bottom out" is showing?

So long as you don't wait forever. The market bottom of any exchange or stock is $0.00. The market, will likely never actually "bottom out". Look into DCA Dollar Cost Averaging. I personally, and professionally, manage DCA strategies with applying additional infusions during obvious lows (example: markets are down 10% in a given period). The bottom of a cycle can undulate "sideways" a bit over a period of weeks, months, years, decades with few discernible entry or exit points. Sometimes after an "event" occurs, the market/stock jumps XX% and opportunities may not occur again in the near future (goes sideways at new level). I note sideways markets/stocks and calculate the risk/reward if I deem it an opportune time. In most markets stocks don't go sideways forever.

I can only offer you my personal opinion, which could well be wrong. I can take no responsibility for what you do with your money.

That said, my opinion is this: there's far more risk than potential reward in the market right now, even after this drop. This is probably the beginning of a bear market that could last, I don't know, anywhere from maybe 6 to 18 months. I would definitely not suggest buying until it's clearly over.

EDITED to add: here's a good summary: http://seekingalpha.com/article/3825236-bear-market-phases-s...

Don't try to time the market, it's a fool's game. Do regular purchases of a broad index ETF (exchange traded fund, low fees!), AKA dollar cost averaging as another child mentions. If you are worried about downswings, keep your portfolio balanced to roughly 50% equities and 50% bonds (there are broad bond index ETFs too).

You don't know. Nobody knows. So you make your best guess, and you don't put all your eggs in one basket.