For a while, I watch the line ahead of me. As usual, the gaps are widening. I shake my head. If I can't even deal with this in a simple hike, how am I going to deal with it in the plant?
What went wrong back there? Why didn't the balanced model work? For about an hour or so, I keep thinking about what happened. Twice I have to stop the troop to let us catch up. Sometime after the second stop, I've fairly well sorted out what happened.
There was no reserve. When the kids downstream in the balanced model got behind, they had no extra capacity to make up for the loss. And as the negative deviations accumulated, they got deeper and deeper in the hole.
Then a long-lost memory from way back in some math class in school comes to mind. It has to do with something called a covariance, the impact of one variable upon others in the same group. A mathematical principle says that in a linear dependency of two or more variables, the fluctuations of the variables down the line will fluctuate around the maximum deviation established by any preceding variables. That explains what happened in the balanced model.
Fine, but what do I do about it?
On the trail, when I see how far behind we are, I can tell everyone to hurry up. Or I can tell Ron to slow down or stop. And we close ranks. Inside a plant, when the departments get behind and work-in-process inventory starts building up, people are shifted around, they're put on overtime, managers start to crack the whip, product moves out the door, and inventories slowly go down again. Yeah, that's it: we run to catch up. (We always run, never stop; the other option, having some workers idle, is taboo.) So why can't we catch up at my plant? It feels like we're always running. We're running so hard we're out of breath.
I look up the trail. Not only are the gaps still occurring, but they're expanding faster than ever! Then I notice something weird. Nobody in the column is stuck on the heels of anybody else. Except me. I'm stuck behind Herbie.
Herbie? What's he doing back here?
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I lean to the side so I can see the line better. Ron i's no longer leading the troop; he's a third of the way back now. And Davey is ahead of him. I don't know who's leading. I can't see that far. Well, son of a gun. The little bastards changed their marching order on me.
"Herbie, how come you're all the way back here?" I ask.
"Oh, hi, Mr. Rogo," says Herbie as he turns around. "I just thought I'd stay back here with you. This way I won't hold any- body up."
He's walking backwards as he says this.
"Hu- huh, well, that's thoughtful of you. Watch out!"
Herbie trips on a tree root and goes flying onto his backside. I help him up.
"Are you okay?" I ask.
"Yeah, but I guess I'd better walk forwards, huh?" he says. "Kind of hard to talk that way though."
"That's okay, Herbie," I tell him as we start walking again. "You just enjoy the hike. I've got lots to think about."
And that's no lie. Because I think Herbie may have just put me onto something. My guess is that Herbie, unless he's trying very hard, as he was before lunch, is the slowest one in the troop. I mean, he seems like a good kid and everything. He's clearly very conscientious-but he's slower than all the others. (Some- body's got to be, right?) So when Herbie is walking at what I'll loosely call his "optimal" pace-a pace that's comfortable to him -he's going to be moving slower than anybody who happens to be behind him. Like me.
At the moment, Herbie isn't limiting the progress of anyone except me. In fact, all the boys have arranged themselves (delib- erately or accidentally, I'm not sure which) in an order that allows every one of them to walk without restriction. As I look up the line, I can't see anybody who is being held back by anybody else. The order in which they've put themselves has placed the fastest kid at the front of the line, and the slowest at the back of the line. In effect, each of them, like Herbie, has found an optimal pace for himself. If this were my plant, it would be as if there were a never-ending supply of work-no idle time.
But look at what's happening: the length of the line is spreading farther and faster than ever before. The gaps between the boys are widening. The closer to the front of the line, the wider the gaps become and the faster they expand.
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You can look at it this way, too: Herbie is advancing at his own speed, which happens to be slower than my potential speed. But because of dependency, my maximum speed is the rate at which Herbie is walking. My rate is throughput. Herbie's rate governs mine. So Herbie really is determining the maximum throughput.
My head feels as though it's going to take off.
Because, see, it really doesn't matter how fast any o ne of us can go, or does go. Somebody up there, whoever is leading right now, is walking faster than average, say, three miles per hour. So what! Is his speed helping the troop as a whole to move faster, to gain more throughput? No way. Each of the other boys down the line is walking a little bit faster than the kid directly behind him. Are any of them helping to move the troop faster? Absolutely not. Herbie is walking at his own slower speed. He is the one who is governing throughput for the troop as a whole.
In fact, whoever is moving the slowest in the troop is the one who will govern throughput. And that person may not always be Herbie. Before lunch, Herbie was walking faster. It really wasn't obvious who was the slowest in the troop. So the role of Herbie- the greatest limit on throughput-was actually floating through the troop; it depended upon who was moving the slowest at a particular time. But overall, Herbie has the least capacity for walking. His rate ultimately determines the troop's rate. Which means-
"Hey, look at this, Mr. Rogo," says Herbie.
He's pointing at a marker made of concrete next to the trail. I take a look. Well, I'll be... it's a milestone! A genuine, hon- est-to-god milestone! How many speeches have I heard where somebody talks about these damn things? And this is the first one I've ever come across. This is what it says:
"- 5-" miles
Hmmm. It must mean there are five miles to walk in both directions. So this must be the mid-point of the hike. Five miles to
go.
What time is it?
I check my watch. Gee, it's 2:30 P.M. already. And we left at
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8:30 A.M. So subtracting the hour we took for lunch, that means we've covered five miles... in five hours?
We aren't moving at two miles per hour. We are moving at the rate of one mile per hour. So with five hours to go...
It's going to be DARK by the time we get there.
And Herbie is standing here next to me delaying the throughput of the entire troop.
"Okay, let's go! Let's go!" I tell him.
"All right! All right!" says Herbie, jumping.
What am I going to do?
Rogo, (I'm telling myself in my head), you loser! You can't even manage a troop of Boy Scouts! Up front, you've got some kid who wants to set a speed record, and here you are stuck behind Fat Herbie, the slowest kid in the woods. After an hour, the kid in front-if he's really moving at three miles per hour-is going to be two miles ahead. Which means you're going to have to run two miles to catch up with him.
If this were my plant, Peach wouldn't even give me three months. I'd already be on the street by now. The demand was for us to cover ten miles in five hours, and we've only done half of that. Inventory is racing out of sight. The carrying costs on that inventory would be rising. We'd be ruining the company.
But there really isn't much I can do about Herbie. Maybe I could put him someplace else in the line, but he's not going to move any faster. So it wouldn't make any difference.
Or would it?
"HEY!" I yell forward. "TELL THE KID AT THE FRONT TO STOP WHERE HE IS!"