If you were developing a garden to feed your family, nothing would potentially give you more anxiety than whether or not it would yield enough to do that, and in the desired timeframes.
Unfortunately, plagues, pestilence and various other events of nature, often unpredictable as to their timing and impact, are constant potential threats. Known unknowns are always out there, as are unknown unknowns.
So it is with your financial garden. Good planning can soften the effects of reverses. Making an early start to building your financial plot is important. Clear eyed constancy of purpose and resolve will undoubtedly be necessary, indeed be imperative, from time to time. But this side of Paradise, and over any reasonable time period, reverses (or at least seeming reverses) of fortune will occur. It is how you approach and deal with these reverses that will determine the ultimate yield from your investment acres.