Why the plan breaks

The usual plan lists everything that should happen and assigns it to days. It breaks because it assumes a week with no interruptions, no overruns and no bad days — a week nobody has ever had. When Tuesday goes wrong the whole structure is invalid, and an invalid plan gets abandoned rather than adjusted.

The fix is to build in the slack the week will actually take. Plan roughly sixty per cent of your available hours. The remaining forty is not waste — it is what absorbs the overruns, and it is the difference between a plan that bends and one that snaps.