Critical path

Take a site launch: design takes two weeks, build takes three and can't start until design is done, QA takes one and can't start until build is done. That chain — design, build, QA — is six weeks long, and no amount of hustle elsewhere makes the project finish sooner. That chain is the critical path. The photo shoot happening alongside build isn't on it; photos could slip a week and the launch date wouldn't notice.

Tasks on the critical path have zero slack: a day lost there is a day lost from the project. Tasks off it can slip, within limits, for free. That single distinction tells you where to spend your attention, where to put your buffer, and which status updates actually matter this week.

Project software will compute the critical path formally, but on a chart with a readable number of tasks you can see it — it's the longest unbroken chain of arrows from the first bar to the last. If you can't trace it, the chart has too many tasks, not too few highlights. If you want the method spelled out, here's how to find the critical path by hand, step by step.