Your mind cannot build deeply while constantly changing rooms.

Deep work requires holding a lot of context at once, and that context is assembled slowly and lost instantly. Every switch means rebuilding, and if you switch often enough you never get past the assembly stage. This is why fragmented days produce shallow output regardless of how many hours they contain.

Protect at least one long block for the work that matters, and treat leaving it as expensive. Notice how different hour three feels from hour one. Depth is a function of continuity, not total time.