It's not impossible, in fact it is inevitable.
Bitcoin only has one enemy: Time
Given enough time a collision will take place with a mathematical certainty.
This does not mean that it is feasible.
The energy and time needed to reverse engineer a key are astronomical.
But that does not mean that it is impossible.

Also i have said it before, cases vary from situation to situation.
I know that there were key's that were already discovered in the lower 64 bit spectrum.
Or take for example the many sha256 hacked brain wallets.
I also know that there are still many robots online that will monitor these wallets and instantly absorb any and all satoshi that arrives there.

You can run around shouting impossible all day long, but it has already been done before and many times actually,
The thing is that these events all happened in less secure situations.
So its fair to say that it is unfeasible under normal strong cryptographic circumstances.
But not impossible it just boils down to a combination of time energy hardware and luck.