That line, (or something like it), borrowed from literature by Murray Gell-Mann, refers to particle physics. Unless a reaction is not allowed (i.e. it violates some conservation law), it will have some probability of occurring, even if the amplitude is small. And you would have to include it in your “sum over all paths” calculations of interactions.
Well, it appears to apply to science journalism as well. Wrenching a statement out of context and misinterpreting it is apparently not forbidden, so a story will appear that just gets it wrong, as so often happens and happened again. Via ZapperZ, I see that there’s a story about the upper mass limit of photons article I mentioned recently, that takes a disappointing tack:
Photons May Emit Faster-Than-Light Particles, Physicists Suggest
Oh, good grief no. That was not “suggested” at all, and certainly wasn’t the point of the paper.
The reference you might be looking for might be T. H. White’s Once and Future King. The law of the hive was Everything not forbidden is compulsory. I think it is one of the tales of young Arthur who has Merlin turn him into an ant as part of his learning about the world by seeing it through non-human eyes. Then again, it has probably been decades since I read the book, and you might have been thinking of some other similar quote.