Two-key sequences (like G B) require the second key within 1.5 seconds. They don't fire if you're typing in an input.
Left-hand-only shortcuts: Most navigation hits the home row. Designed so you can keep your right hand on the mouse for clicking through.
Customize: keys are defined in js/hotkeys.js — fork and remap if you want.
Print this page and stick it next to your monitor. The muscle memory pays compound returns.