This kanji depicts a person (人) falling into the abyss, symbolizing their disappearance or perishing. Imagine the top stroke as the ground and the bottom as a person falling underneath.
'BOU' — Imagine a ship's 'BOW' falling apart and perishing in a storm.
'MOU' — When something is 'lost' or 'perished', you might 'MOAN' in sorrow.