This is a big concept in advanced metrics. Well, actually, you don’t need a big brain, or a fascination with numbers, to grasp this.

If a guy has a history of performing at level X, but for a month he performs at level X+50 percent … it is likely he will find his way back significantly towards level X before his season is over.

We all know this, intellectually. But we often find ourselves looking at the guy who is performing well over his historical norms … and you think, “even if he goes halfway back towards what he’s done before I’m still ahead …”

But that is dangerous, too. Chances are pretty good he is going to go most of the way back … and it also is not unknown that his “regression to the mean” could come quite quickly.

Which leads me to Jake Marisnick.

Marisnick is an outfielder with the Houston Astros.

Before that, he was with the Miami Marlins. He was considered something of a hot prospect, along with a kid named Chris Yelich, and they both came up in 2013, and Yelich did enough to win a place in the lineup, and Marisnick did not.

He was traded to Houston middle of last season, played some, but didn’t seem much different from the guy who played with the Marlins.

And what was he? A guy with some speed, apparently a pretty good outfielder … but a shaky hitter who struck out a lot, didn’t have much power and was likely to hit in the .240 range, with an OBP under .300

Then we came to the opening weeks of 2015.

Through games of May 3, when is when I added Marisnick to my team via our league’s supplemental draft … he was hitting .382 with a .427 OBP.

And there’s more. He had three home runs, had driven in 12 runs and scored 13. He was hitting in the 1 hole more than once in a while.

Plus, he had nine steals in 10 attempts. He was on pace for more than 40 steals, which is huge in our league.

I took him, made clear I expressed my fears that he would regress …

And, oh my goodness, did he ever.

In a span of three weeks, when he was in my lineup, he went about 80 percent of the way back to what he really is.

He lost 101 points off his batting average, to .281. He shed 108 points of OBP, to a league-average .319.

In those three weeks, he hit .167 (10-for-60) with two doubles, four runs, and four RBI. He had two walks against 22 strikeouts.

He actively helped me lose a bunch of games.

And that, ladies and gentlemen is “regression”. A very tidy example of it.

We all like to think the red-hot guy who is playing like he never has before can somehow keep it up, or at least keep up some of it … but no, that is very rarely what will happen.

Too many games in a baseball season. Too many chances for your real baseball self to come back to the fore.

Jake Marisnick … thanks for the object lesson.