발단이 · 발단을
the beginning, the origin, what started it (often of trouble)
Example
작은 오해가 큰 싸움의 발단이 되었어요.
A small misunderstanding was what started a big fight.
Word parts
발 start+단 tip, end
Literally 'start from the tip' — the first end of a thread.
Good to know
In literature class, 발단 is also 'exposition', the first stage of a plot: 발단–전개–위기–절정–결말.
Related words