Running several projects at once feels like progress on all of them. But every switch costs you — reloading what you were doing, where you left off, what comes next. Gerald Weinberg put rough numbers on it: each project past the first sheds about a fifth of your capacity to context switchingThe cost of stopping one task and resuming another: rebuilding the mental state you'd paged out. The more you hold at once, the more of your day goes to the swap rather than the work.. Slide the count and watch the productive time drain.
Of a full day's capacity, 40% evaporates just moving between the projects — leaving 60% that actually reaches the work, about 20% per project.
| Projects at once | Productive time |
|---|---|
| 1 project | 100% · 100% each |
| 2 projects | 80% · 40% each |
| 3 projectsnow | 60% · 20% each |
| 4 projects | 40% · 10% each |
| 5 projects | 20% · 4% each |
Splitting yourself evenly across 3 projects sounds like 33% each — but switching skims another 13% off every one, so each really gets 20%. The cure is the unintuitive one: finish things. Fewer in-flight efforts means less of the day spent paying the swap.