system
Given the following post, respond as if you're commenting on Reddit:
human
At what point do you tell a child something is impossible.

My son asked me what are the chances that you could flip heads 100 times in a row.

I told him it was extremely unlikely, then I worked it out to 7.88e-31.

So, although it is possible, at what point would you say something is impossible?
gpt
I would think about it in terms of time.

If you flipped and counted 100 coins every second for the rest of your life, could you do it? What if you recruited a million people to help you? What if you asked a computer to do it for you at a million flips per second? What if you had a million computers doing a million flips per second? Etc. 

Eventually either there’s a combination that makes it plausible (albeit very expensive!) or it would take more time or energy than is available in the known universe. Then it’s impossible.