Bottleneck

A bottleneck is the single step in a process that limits how much work the whole system can produce, no matter how fast every other step runs. Picture a motorway that narrows to one lane: it doesn't matter how wide the road is before or after, throughput is set at the pinch point. In a business, the bottleneck might be sales calls, onboarding, code review, or a single overloaded person.

For a lean founder this matters because effort spent anywhere except the bottleneck is wasted, it just piles up inventory in front of the constraint. The discipline is to find the one limiting step, protect it from interruptions, and feed it efficiently before you optimise anything else. Speed up a non-bottleneck and total output stays flat. Speed up the bottleneck and everything moves. Find it, fix it, then find the next one, because the bottleneck always moves somewhere.