You feel mentally drained with too many apps open on your Mac because your brain treats each one as an unfinished task demanding resolution.

Every open application, whether you're actively using it or not creates what psychologists call an "open loop" that consumes working memory in the background. Your brain can't distinguish between "I'm not working on this right now" and "this needs my attention."

You're mentally exhausted by midday not because your tasks were difficult, but because your environment forced you to make hundreds of invisible decisions before you even started the real work. Every time you switch contexts on your Mac opening the right apps, finding the right windows, arranging your workspace you're burning through the same cognitive resource pool you need for focus, creativity, and willpower.

Decision fatigue is the deteriorating quality of decisions made after a long session of decision-making. Your prefrontal cortex has a limited daily budget for choices, and once it's depleted, everything from strategic thinking to basic self-control becomes harder.

The biggest focus killer isn't a notification; it's leaving your desk. When you switch from Mac to iPhone, your focus context disappears. Apple's Focus Modes sync Do Not Disturb across devices but don't preserve what you were working on. The fix is pairing a workspace manager (for your Mac environment) with a focus companion (for your phone) so your focus state survives the device switch.