OK, so I get that you can lose Magic/Resonance as you lose Essence. But how else can it happen?

I think I remember reading something about "losing confidence" when you glitch, but I can't find it in SR4 or Street Magic for the life of me. Anyone got any ideas?

Also, do you lose it when you take a Deadly wound (well, OK, fill your Physical Condition Monitor)?

The thing you're looking for is in Street Magic. Don't have the book with me, but I know it's there. It's under the Geas part. It goes something like this...

When you have a geas, you have to do something to cast a spell. While you don't HAVE to use that geas, it helps you cast better. However, when you critically glich, you take a hit to your confidence and can't cast as well. You temporarily have lower magic, I believe. So, you have to try and center yourself again. However, if you try again to cast without the geas and critically glitch once more, you just sucked up a magic point as you begin burning out.

Ah right, thanks! That seems spectacularly unlikely to happen, though. And there's no risk of Magic loss from stim addiction any more, is there?

No Magic loss from Stims or Damage in SR4. The section you want in Street Magic is on page 30

Oh yes there is. Addiction, BBB p. 80. A character loses 1 Essence if/when addiction reaches Burnout level, and continues to drop at GM-governed levels until the character dies or pulls out of Burnout. Essence loss will have the side effect of Magic loss. Doesn't matter whether the addiction is stims, alcohol, BTLs or other, as long as it's something unhealthy.

Yes, but that is from Addiction, not Stims or Damage specifically, which were two things that could indeed directly cause Magic loss in previous editions.

I hated that with my adepts, take a D wound roll for magic loss. Damn I lost one point. Geas it! Damn broke my geas Lose my magic point.

Viscious circle.