Your Thumb Is the Primary User

Hold your phone in one hand and try to tap the top-left corner. That reach — the little shimmy where you loosen your grip and the phone teeters over the pavement — is a design decision someone made for you. Research on how people actually hold phones has found one-handed use accounts for roughly half of all interactions, and the comfortable thumb arc covers barely a third of a modern 6.7-inch display: the bottom third, biased to the thumb's side.

Everything above that arc is, functionally, a two-handed zone. Which is fine — until you put the thing the user needs most in it.

Map any screen into three zones. The natural arc at the bottom: effortless, where the tab bar lives and where primary actions belong. The stretch zone across the middle: reachable with grip adjustment. The hostile zone at the top corners: the traditional home of navigation, back buttons, and 'Done'.

The platforms have quietly conceded. Gesture navigation moved 'back' to a swipe. Apple shipped Reachability — an OS-level apology that drags the top of the screen down to your thumb. Search fields migrated to the bottom in Safari and Maps. The direction of travel is unambiguous: interfaces are sliding down the glass toward the hand.

The accessibility frame makes it sharper. For a user with limited grip strength, a wheelchair user working one-handed, or anyone with a limb difference, the hostile zone isn't awkward — it's absent. Design for the thumb arc and you aren't optimising for laziness. You're designing for the actual, physical range of the actual, physical user. The corner was never yours.