Here’s an easy question for you. You need to win the next two baseball games. All else being equal, would you rather start Clayton Kershaw and Zack Greinke, or Clayton Kershaw and Dan Haren?

Right, okay. Couldn’t be simpler. Greinke’s better than Haren is, so you opt for the former. And that’s what the Dodgers are doing in the NLDS against the Cardinals — instead of starting Haren in Game 4 and Kershaw in Game 5, they’re starting Kershaw in Game 4 and planning to start Greinke in a potential Game 5. As it turns out, according to Don Mattingly, this was always the plan, and Haren was only penciled in for Game 4 in case Kershaw didn’t look great after his first start. But as you know, there’s a twist to this. It’s not just Kershaw/Greinke vs. Kershaw/Haren. It’s ~Kershaw/Greinke vs. Kershaw/Haren. And that ~ makes all the difference.

Kershaw is starting today on a day less rest. By pushing him up, ahead of schedule, Greinke would be available on regular rest. One should note, in fairness, that Haren hasn’t pitched in a game since September 27. So, maybe there’s a long-rest penalty. But we know more about the short-rest penalty.

Conveniently, the Dodgers did this exact same thing a year ago, and I mean precisely a year ago, going with Kershaw on short rest over Ricky Nolasco. So that made the equation ~Kershaw/Greinke vs. Kershaw/Nolasco. I wrote about that at the time, and I might as well blockquote myself:

Below, you’ll see statistics for two groups, in postseason play between 1995-2013. The first group is starters who went on three days’ rest. The second group is starters who didn’t. Understand that the first group should be selective for better arms, because you don’t put mediocre starters on short rest in October, or ever. Typically, it’s aces who go on three days’ rest, and the numbers are telling:

Short-rest group: 4.66 ERA, 5.13 RA
Other group: 3.99 ERA, 4.30 RA

On short rest, starters have faced fewer batters, on average. They’ve posted worse game scores, on average. And — maybe most importantly — teams with starters going on short rest have won 33 times and lost 52 times. Now, maybe these teams are worse, which is why they’re starting guys on short rest in the first place, but they’ve by and large given the ball to their aces, and the aces haven’t delivered like usual.

Pitchers in the playoffs lately have been worse on short rest. For the most part, these were pitchers selected because it was believed they’d be good on short rest. It’s been demonstrated, in particular in The Book, that pitchers suffer on short rest, relative to regular rest. So you expect the odds of success to be lower. You lower your expectations. It’s always a case-by-case basis, but when you look at the cases together, you see some separation.

Of course, there’s that other thing. That one most pertinent data point. On three days’ rest, last October 7, Kershaw threw six innings against the Braves, throwing 67% strikes and allowing two unearned runs. The Braves’ two-run inning featured a line-drive single, a groundball single, an error on the first baseman, and a wild pitch. Kershaw whiffed six before being removed after 91 pitches, and his velocity and movement were normal. Indications were that Kershaw was just fine.

And he was fine his next time out. But one data point isn’t more important than a whole group of similar data points, and in Kershaw’s next start, on October 18, he allowed seven runs in four innings. Short rest doesn’t only have an effect the day of — it’s been suggested the effects can linger or show up down the road, as you haven’t allowed your body to fully recover. It’s possible that starting Kershaw early was in part responsible for the bad start a week and a half later.

Arranging things this way lines Kershaw up sooner for a potential NLCS. He’s also presumably learned some things from his first short-rest experience last October. Maybe it benefits Kershaw that he missed time early this season, so there are fewer 2014 miles on his arm. There are innumerable variables here, and the Dodgers believe that Kershaw is up to the task, so we almost have to defer to them. They see the good here. But the history of this is mixed, and real good pitchers have turned in real bad games after resting three days. Clayton Kershaw will be on the mound, but there’s a greater chance he will not be himself. Maybe, instead of throwing 80 out of 100 pretty good pitches, he throws 75 out of 100. Maybe those five pitches are everything. Maybe those five pitches are nothing.

Here’s one way you might be able to think about this and relate to this. There are very few things more important to you than sleep. Maybe nothing’s more important, at least among the things under your own control. Sleep is still a very active field of research, but it’s been demonstrated several times over that getting enough sleep is good for your health, and your mood, and your productivity, and your everything. Sleep is amazing. We should all want to protect our sleep hours, but we’ve also all functioned on less sleep than is recommended. For whatever reasons, we’ve had nights where we’ve had to sacrifice hours, and then the next day we’ve had to function.

Sometimes everything seems fine. Sometimes the next day is awful. You might feel your brain lagging, you might feel less creative, you might be quicker to temper. I’ve written decent baseball articles on little sleep, and I’ve written awful baseball articles on full sleep, but on average, we have better days after sleeping well. If disruptions pile up, it’s worse, and several nights of bad sleep are worse than one night with bad sleep, but if you examine enough people, the day after not sleeping well, they’ll perform below their norm. Maybe not dramatically, and when you have a bad day you might not automatically blame it on not spending enough time in bed, but the effects can be both very subtle and very real.

Usually, if you have to lose some hours of sleep, you don’t freak out. You know you can manage, because in the past you’ve managed well enough. Maybe sometimes there’s been no difference at all. You don’t change your expectations for the day because you slept for five hours instead of seven or eight. But you’re more likely to be different, and worse than yourself, and if we don’t think about that enough, maybe it’s because we still underestimate the importance of rest.

Clayton Kershaw, basically, is going to work after a shorter night than he’s used to. He’s still going to look like himself, and he’s still going to demonstrate the same general skills. If there’s a difference, it might only be at the margins. But then, sometimes baseball’s all about the margins. Everybody in the game has got the talent.