a fly on the wheel的用法和样例：
- Peter is nothing but a fly on the wheel.
- He is a ruler without power, a mere fly on the wheel.
- She could not help thinking that he was breaking a fly on the wheel.
- She could not help thinking that he was crushing a fly on the wheel.
- I wish I could be a fly on the wall when they discuss my future.
- He was only a fly on the wheel.