Full Kelly assumes your win probability is exactly right; taking a quarter of it trades a little long-run growth for a lot of protection against being wrong about your own edge.
TODO — write this one yourself.
TODO — cover what Kelly actually optimizes, why estimation error and not variance is the real risk, and why a hard 3% cap sits on top of the formula.
Math, not advice. 21+ where legal. If gambling stops being entertainment, call 1-800-GAMBLER.