What is the hardest thing about public speaking?

For some people, public speaking is their number one fear. But some people have no problem speaking in public. A lot of people are in the middle. Some are comfortable speaking to small or medium-sized groups but not large groups. Some do well if they have time to prepare their speeches but not so well if they have to speak impromptu. Many could benefit from incorporating techniques such as vocal variety, more eye contact or energy during their delivery but they're scared to step outside of their comfort zone. No matter how much practice or experience you have speaking publicly, you can always get better. I watch for audience feedback when I speak to help me to get better. I never get bored with the process because every audience is different. One audience may love your presentation but another audience may get bored with you. This keeps me on my toes and ensures that I never take any speech for granted. Some people may think the unexpected of public speaking--not knowing what to expect from an audience--is the hardest thing about it. I would love to hear what you think is the hardest thing about public speaking.