It is difficult, if not impossible, to memorize 20,000 consecutive numbers.
An impossible task, an impossible request.
You never listen to a word I say – you're impossible!
Walking to the moon is an example of something that would be described as impossible.
Someone who is really demanding, and who is never pleased no matter what, is an example of someone who would be described as impossible.
An impossible goal.
An impossible child; an impossible situation.
If we work together, we can achieve the impossible!