I was recently answering this question and for some reason it made me think of this fairly famous aviation saying
The three most useless things to a pilot are the altitude above you, runway behind you and fuel on the ground
Now, I get altitude above you - you may as well use some of it lest you meet a mountain. I also get fuel on the ground - if in any doubt fuel up before you go.
But I'm not sure I understand why "runway behind you" is useless in this context
Could someone explain?