Not 'excellently' — 'without snagging'

Where the picture shows up in 잘

1. 1

   time that rolled by without trouble

   그동안 잘 지내셨어요?

   geu-dong-an jal ji-nae-syeo-sseo-yo

   How have you been?

2. 2

   not coming through smoothly

   소리가 잘 안 들려요.

   so-ri-ga jal an deul-lyeo-yo

   I can't hear you well.

   Not about bad ears — the sound isn't arriving smoothly.

3. 3

   a skill that runs smooth

   한국말을 참 잘하시네요.

   han-gung-ma-reul cham jal-ha-si-ne-yo

   Your Korean is really good.

4. 4

   a frozen set phrase

   잘 먹겠습니다.

   jal meok-get-seum-ni-da

   Thank you for the meal.

   Said before eating; nobody is literally promising to eat 'excellently'.

5. 5

   before a negative: 'not exactly'

   저도 잘 모르겠어요.

   jeo-do jal mo-reu-ge-sseo-yo

   I don't really know either.

   잘 몰라요 is closer to 'I'm not sure' than to 'I have no idea'.