I make you weak at the worst of all times. I keep you safe, I keep you fine. I make your hands sweat, and your heart grow cold, I visit the weak, but seldom the bold. What am I?

Why this works

This riddle cleverly plays with the various aspects and effects of fear. The first line hints at how fear can incapacitate us during crucial moments, making us feel weak. The phrases "I keep you safe, I keep you fine" reveal that fear can also serve a protective function, alerting us to danger. The imagery of sweaty hands and a cold heart captures the physical reactions to fear, while the last line contrasts the experiences of the timid versus the courageous, emphasizing that fear often affects those who are less bold. All these elements come together to encapsulate the multifaceted nature of fear, making it the perfect answer to the riddle.