이 떨어지면

if it falls off

→ 이

phrase Uncommon #7,155

if it falls off The subject particle 이 attaches to a noun, and 떨어지면 is the conditional form of 떨어지다. Depending on context, it can also mean “if it runs out,” as with ammunition or supplies.

KO: 나뭇잎이 떨어지면 겨울이 온 거예요.

EN: If the leaves fall, it means winter has come.

만약 기름이 떨어지면 어떡할래?

What if we run out of oil?

— 아메리카의 밤 (1973)

빵이 떨어지면?

What happens if the bread runs out?

— 물랑루즈 (2001)