I should have mentioned that investing comes with the caveat that one should also have a plan for major life events like a job loss. Having 6+ months of living expenses on hand in cash is a must. I firmly believe that 70%+ of the stress and anxiety of losing one's job is the pressing need for cash flow. I can't imagine the kind of stress that produces for someone who lives paycheck to paycheck.
That brings me to a larger (slightly off-topic) point: people don't save enough money. 10% is the absolutely minimum one should be saving, despite that being the common advice which no one follows. Most people, even high-earners, spend nearly all of their money. There are tons of people out there making $75k+ per year who are a couple paychecks from being on the street. Those people are simply doing it wrong and will absolutely get bit in a down market.
For those still reading, do this: Get an emergency fund that you can live on for 6+ months. Pay off your debts. Contribute to your IRA, 401k, or whatever else, putting all of that money into a boring index fund that tracks the market (I like VTSAX because Vanguard's fees are incredibly low). Make sure at least 20% of your money is invested. The only people who this might not work for are those earning at or near minimum wage with dependents. If you're not in that group, just do it. You do not need that 20% of your money right now. You may think you do, but you don't. You're spending money on stuff you don't need.
My apologies for getting so far off topic. This is just something I feel very passionately about.