编者按：这是Quora上一个有趣的问题。以下是得到的赞同数最多的答案。

1. I would not date anyone. It was a total waste of time.

2. Work on getting better at skills important to sustain in life and become successful.

3. I'd excercise and work out to feel more healthy.

4. I'd not try cigarettes.

5. I'd be more organised.

6. I'd start saving money.

7. I'd be nice to each and every person and keep my ego aside.

8. I’d start reading books and improve how I write.

9. I'd learn how to cook and eat healthy.

All of the above are things I realised now when I'm 25. I know it's not been long since I was 20 but I always feel like I wasted so much of my time.