The number was green and the line was standing still.

Every target you set will be hit. The question is what gets broken on the way to hitting it, and whether you are watching that too.

Early in my career I worked on a tissue line. A parent reel, a tonne in weight and three metres wide, was unwound and rewound into the small rolls everyone recognises. The rewound lengths went to a saw, were cut into rolls, and travelled down an automated line to be packed.

The measure that ran the line was speed. Metres per minute. The logic was sound on its face: faster line, more rolls, more product shipped. So the target was speed, the operators chased it, and they hit it.

And the line kept stopping.

Here is what the speed number could not see. Running the rewinder faster affected the glue that sealed the end of each roll. At higher speeds the seal did not form cleanly, and rolls came off with loose tails. The tails were invisible to the speed measure. But as the rolls went down the line the tails caught, tripped the sensors, and jammed the packing machines. The packing line backed up. The buffers filled. The backup forced its way upstream until the rewinder itself had to stop.

So the line ran fast, made rolls that could not be packed, and stopped. On the board the speed target was met. The number was green and the line was standing still.

Nobody was gaming anything. The operators did exactly what the measure asked. The measure asked for the wrong thing on its own, and the system delivered exactly that: a perfect headline number sitting on top of a stopped line.

Every primary measure needs a second one beside it, the measure that catches the harm the first one causes when it is chased alone. Speed needed rolls successfully packed, or line uptime, in the same glance. With that pair in place, the operator chasing speed sees the cost of the tails and backs off before the line stops. Without it, the board stays green while the output collapses.

When you set a target for a change, the question is not only which number means success. It is which number this one will quietly wreck, and how you will watch both at once.

What is the number on your board that is green while something behind it has stopped?