请提供一句富有哲理的名言，并以markdown格式输出。该名言需要包含关于时间和机遇的关系。名言的作者也可以是虚构的。 ```markdown
> "名言内容"
> —— 作者名
```
user
```markdown
> " time, like an opportunity, is a revolutionary ally that may never knock twice; seize it in its first fleeting moment. "
> —— Cassandra Nova
```
assistant