James 4:14 compares your life to what, which appears briefly and vanishes?

Answer: A mist

"What is your life? You are a mist that appears for a little while and then vanishes" (KJV: a vapour).

“You do not even know what will happen tomorrow! What is your life? You are a mist that appears for a little while and then vanishes.”— James 4:14 (BSB)