[abhorrence]

“All but X” is an idiom in (at least American) English which means essentially “99%”. So in this case it didn’t literally cure his insomnia, but is so close to having done so that it may as well have.

[mewpmewp2]

It just sounds somehow so wrong to me, I'm not a native speaker though.

[rexer]

Native speaker here, this has kept me distracted on a couple long drives.

  “X is all but Y”

  Interpretation 1: X has moved so close to Y that it may as well be Y  
  -> X loosely equals Y   
  (I think this is the colloquial understanding)

  Interpretation 2: In the set that represents X, Y has been removed  
  -> X is not Y

Excuse the poor notation, I hope this is clear! The tldr is this confuses me too sometimes

[mewpmewp2]

Yeaaah. But it feels like "all" could be everything that is positive OR negative, so if you have all the positive and all the negative, and you take the one positive away (or the most positive), it is slightly negative (or very negative)?

[rexer]

Yea! I thought along the same lines, but I wasn't sure how to write it out. If X is on a spectrum, and Y is removed, it's closer to not-Y.

Edit, eh your explanation probably explains it better anyway :)

[mewpmewp2]

I really appreciate your positive responses to my off-topic out-of-blue observations.

[everforward]

It throws me off because it sounds sarcastic depending on which parts you emphasize. "The fire department all but put out the fire".