In my hometown of Baltimore, there’s an oft-heard saying that seems especially applicable when, like now, the seasons are changing: “If you don’t like the weather today, just wait until tomorrow.” For whatever meteorological reason, it’s not uncommon for an absolutely miserable Monday to turn into a gorgeous Tuesday. Temperatures have been known to swing as much as 20 degrees inside of an afternoon.

A scientific view of stock market history, unfortunately, shows us an even greater propensity for unpredictability and volatility.

Even the years that we refer to as the “good” ones, in retrospect, test our mettle. For example, between 1950 and 2014, a span of 65 years, the S&P 500 ended the year with a gain 51 times (or in almost 80% of them). Not bad. But in how many of those up years do you think investors would’ve found themselves in a “losing” position at some point in the year?

Every. Single. One.