What does it mean that externalization reduces cognitive load?

Example: You're an engineering lead reviewing a pull request while simultaneously holding three unresolved architecture decisions, a staffing concern, and a deadline you haven't communicated. You read the same function four times without absorbing it — not because the code is complex, but because your working memory is full. You're trying to run a six-slot program on a four-slot processor. The moment you write the three architecture decisions on a sticky note and put the staffing concern in a to-do, the code review becomes trivially easy. Nothing about the code changed. You freed the registers.

Try this: Set a 5-minute timer. Write down every open loop currently consuming background processing in your head — decisions pending, tasks remembered but not recorded, worries, half-formed plans. Don't organize them. Just dump. When the timer ends, count the items. Now pick three and externalize each to a specific system: a task manager, a note, a calendar entry. Notice the felt sense of relief. That relief is working memory being returned to you.