the idea is: if we do find life elsewhere, especially basic life, it suggests that getting to that stage isn't super rare. which means the great filter probably isn't behind us (like abiogenesis or single-cell to multi-cell jump), but possibly ahead of us - maybe in surviving long-term, avoiding self-destruction, spreading beyond one planet, etc.

finding life doesn't eliminate the great filter - it raises the unsettling possibility that we haven't hit it yet.