It is absolutely akin to gambling and should only be considered when someone has excess money. Excess money occurs only after the following has taken place and in this order (1) all credit card debts have been satisfied (2) you own your own home (3) you are contributing the maximum amount to your 401 (k) or IRA plan (4) you have paid your mortgage off in your home.
Also, by following the four steps above you get a whopping guaranteed return on your money - as opposed to no guaranteed return when buying/selling stocks. Credit card debts? High rate of interest with no tax deduction. Stop credit card debts and that equates to an effective rate of return in the 20% range with zero risk.
Own your own home? Yes, we all understand what has happened to housing prices. But do you think paying rent is better. Over the course of a lifetime, if you do not own your own home, you will be paying someone else more in rent than you would be paying in a mortgage. And, if you rent, you will own nothing at the end.
401 K or IRA? You do that for three reasons. (1) You get an immediate tax deduction (2) The money you earn on your contributions is tax deferred and (3) When you retire you most likely will need that additional income.
Pay off your mortgage? Most people don't understand why this is a better investment than buying/selling stocks. I'll tell you why. No risk - guaranteed return. You are in essence paying yourself and in the end you will own your home free and clear. Just remember - not having to pay someone else a mortgage is the same thing as earning the money. This is often overlooked.
But what if you have met all the criteria above and you still have excess income that you could invest. In that case, check out my hub: Investment Strategy - Earn 20% Now
and do it the right way.