The core distinction
Box breathing is symmetrical: equal counts across inhale, hold-in, exhale, hold-out. 4-7-8 is asymmetrical: a short inhale, a long hold, and an even longer exhale. That structural difference maps directly onto their physiological effects.
Symmetrical patterns produce composure. Asymmetrical long-exhale patterns produce downshift. You cannot swap one for the other without changing what happens in your body.
When box wins
Before deep work. Between meetings. In the huddle before a play. Backstage during Q&A. Any situation where you need to be sharp and calm at the same time.
When 4-7-8 wins
Pre-sleep. During 11pm rumination. During the aftermath of a stressful event. Any situation where the goal is unambiguously to lower arousal, and where being a little sedated is acceptable or desirable.
Common mistakes
Using 4-7-8 for focus is the most common mistake — the long exhale plus hold makes you sleepy, which is exactly wrong for focus. The reverse mistake — using box breathing to fall asleep — is less common but happens. Box breathing does not put you to sleep.