MENTAL MODEL
Keyboard shortcuts are a grammar, not a word list. Understand these seven rules and you already "know" dozens of shortcuts you never learned.
RULE 1/7
Same arrow - the modifier only sets the size of the jump.
A bare arrow moves one character. Add one modifier - you jump a word. Add the big modifier - you jump a line or the whole document. You're not learning 8 shortcuts, you're learning one ladder with 4 rungs.
RULE 2/7
Any movement you already know + Shift = selecting that movement.
There are no separate selection shortcuts to learn. Know how to jump a word? The same shortcut with Shift selects a word. Know how to jump to the end of the line? With Shift it selects to the end of the line. Movement × Shift = selection, always.
RULE 3/7
The same movement modifiers work with Backspace.
Backspace alone deletes one character, because a bare arrow moves one character. With the word modifier - it deletes a word. The ladder logic repeats here, so there's nothing new to memorize.
RULE 4/7
Line operations work from anywhere in the line. Cursor inside? That's enough.
Deleting, duplicating, moving or commenting a line never requires selecting it first. The editor knows which line you're on. Select-then-act on a whole line is almost always wasted work.
RULE 5/7
When the same word repeats - select the occurrences, don't run to them one by one.
D adds the next occurrence of whatever is under the cursor, and from there you type into all of them at once. Grabbed one too many? U steps back. Need them all? L selects everything in one press.
RULE 6/7
Two swaps explain almost everything.
Mac's Option is Windows' Ctrl for word jumps. Mac's Cmd splits in two on Windows: Ctrl for actions (save, find, undo) and Home/End for line edges. Understand that mapping and you can move between machines without relearning anything.
RULE 7/7
Trusting Undo is what lets you work fast.
Fear of breaking something is what sends your hand back to the mouse. Every action in this game - deleting a line, replace-all, editing in several places - is reversible in one press. Try it, look, and if not - undo.