Whatever you do with your money is a gamble, since nobody knows the future.
Even if you hold all of it safely under your mattress guarded by you, your guns and your dogs, you risk the value of the dollar failing to keep pace with inflation, so your $1,000 under your mattress today may only buy you $500 worth of stuff some time down the road. You just lost 500 bucks when nobody actually even stole anything from you!
Yes, it's true that recently you may have done OK with your $ under your mattress. But, hey, banks are still paying some interest, and that's better than you're getting with it under your mattress.
The saying is: "The only free lunch is diversification". Put part of your money under your mattress, part in a savings account, part in CD's, part in stocks (stock mutual funds actually), part in bonds, and part in real estate (if you can). This way, for whichever part is faltering, you've got other sources that aren't. This is the best you can do without gambling it all on any one of these.
A lot of people's problem is that they pick one of those, think they've got it all figured out, go "all in" on it, and then it falters, and they're bitchin' and moanin' about how bad they got done wrong.