In terms of _quickly_ learning self-defense, I think you need a school that does a lot of dynamic rather than static drills. As everyone has already said, it's impossible to predict how you will react in a real fight, so your training needs to simulate an actual fight as much as possible. You need drills that involve throwing or blocking multiple techniques: most attackers won't stop if you land one punch. You also need partners (or instructors) that are willing to be aggressive during the drills: most attackers want to _hurt_ you, so if your partner just goes through the motions, you won't benefit as much. I think TKD does have great self-defense applications, but if you want to quickly learn to fight (and 4 - 5 months is a pretty short amount of time) then I would suggest studying Krav Maga or boxing - something that emphasizes facing an opponent rather than forms that emphasize the "art" of MA.
