When assessing habitability, what factor often acts as the key disqualifier for a planet located in the HZ?

Answer

Stellar activity

While being in the HZ is necessary, stellar activity often acts as the disqualifier, as a planet orbiting a hyperactive star is unlikely to sustain life regardless of its orbital position.

When assessing habitability, what factor often acts as the key disqualifier for a planet located in the HZ?
astronomystarsexoplanetslifeHabitability