There’s no such thing as an infallible plan, but you can always work toward the next best thing.
The scary thing about the future is that it is almost guaranteed to be accompanied by change. What kind of change? I dunno, no one does. One minute, everything makes sense, the next, everything’s been turned completely on its head. You can make statistical assumptions, but the fact of the matter is that nobody can predict the future with 100% accuracy. It’s for this reason that your finances need to be as future-proof as you can feasibly manage. If you’ve got your ducks in the proper row, then even when change comes knocking, you can maintain your money.
First, make a diverse plan. Anyone can just save money, but unless you’re saving for something in particular, that money’s not going to do anything for you. Do you want to buy a house? A car? Some other large purchase? It doesn’t especially matter what you’re shooting for as long as you’re shooting for something. Having a goal in mind makes planning easier in general. If that plan includes investments, make sure to keep your portfolio diverse. Like I said, you can’t predict when things are going to suddenly go sideways. If one investment goes belly-up, then you’d better have five more to take its place, hydra-style.
However, there are non-business curveballs you need to keep in mind. Medical expenses, for example, have a nasty habit of sneaking up on you. Even if it takes a bite out of your plan, make sure you have contingencies and insurance in place to mitigate those costs. You’ll be relieved to have dental insurance when your tooth randomly chips and don’t have to pay $300 out of pocket for a filling.
Above all, try not to keep your finances static. Keep your money moving all over the place. Make investments, keep your ear to the ground. Ideally, you want any contributions you make toward your goal to reflect your current status. If you’re firmly in the green, put the money toward your goal and savings. If you’re in the red, redirect the flow to eliminating debt and keeping the books even. Saving is not a passive thing that just happens, you gotta manage it like an army.