&gt; <i>That uncertainty is never built into the mathematical model used by project managers</i><p>It depends on the project manager.<p>The PERT estimation technique was based on giving a 3-part range estimate for broken-down tasks. These are then rolled up with a simple formula.<p>In the PERT method independence is handled by creating explicit links between tasks, which leads to the concept of the critical path.<p>Nobody does these. Because it&#x27;s very tedious. There are a lot of tasks for which &quot;just try it and see&quot; is less effort than performing a full-blown estimation raindance.