I have no idea who said it first, but it is a witticism so incisive it nearly draws blood, yet so pithy and droll that it has all the sophistication of a fine wine: “The difference between theory and practice is that, in theory, there is no difference.” To me, the stark accuracy and exquisite elegance of this statement convey ever so much more nuance than talking about “where the rubber meets the road.”
When I think of the difference between theory and practice (hereafter called “The Diff”) in my musical and audio life, I get a flaming vision, shooting incredibly painfully from my third eye, of Practice being the result of Theory having been strapped onto the wild tiger of Reality and left with no alternative other than to ride. But that's just me.
Nonetheless, this points up that point of view determines the perceived point of The Diff. The theoretician and the day-to-day trenchmeister might both view The Diff as a sort of margin of error, but the theoretician's frame of reference casts it as error relative to the mathematical representation, while the trenchmeister understands it as error in the context of an accurate model of the how the world really works.
Even a value judgment on whether The Diff is good or bad depends on frame of reference. If you're producing a live show of any type, performing audio post, or doing most commercial audio-production tasks, deviation from the theoretical model is more often than not a pain in the patootie, though it can be occasionally cleverly leveraged to sidestep a limitation. (“Hey, that's not supposed to work!”)
For the most part, professionals who are in these positions are quite well aware of how extremely relentless the battle is just to hang on to that tiger, and they make broad accommodations for it with redundant systems, contingency plans, and overbuilt equipment. In studio work, this same caution manifests itself in things like a well-founded fanaticism for backing up data. But it is in any kind of real-time function, such as broadcast or live performance, that roadies and technicians give wide berth for a panoply of bizarre eventualities. The whole Boy Scout routine and all that.
On the other hand, much of the art of improvised live performance, music composition, and even sound design lies in the realm where real-world practice departs from theory.
There is another, higher-level argument in favor of The Diff, which hinges, as well, on point of view. Theory can provide a long view and move fast, like a rock skipping on the surface of a lake. Practice, on the other hand, accomplishes what Theory only dreams about. Paradoxically, the most fruitful results occur only when the two have some occasion to meet and intermingle.
Without that meeting, one has experiences like those described in the classic comments of many design engineers when they are exposed to the desires and complaints of customers. While working on a post-production studio for a network TV series, one design engineer, dragged into the field by his director of marketing, informed us that professionals didn't do what we asked for. The director of marketing shot him a look, informed him in a low voice that we were professionals, and tried to salvage the situation.
Conversely, I've seen product specialists trying to explain to practitioners (who wanted to do things the way they'd always done them) how examining their practices closely would reveal an underlying theory that, if explored a bit further, could lead them to discover more efficient methods.
In many cases, The Diff comes about because of limitations in the field. Time and money are, of course, the most common, but logistical, acoustical, infrastructural, and resource limitations also can come into play. Then, it all comes down to the resourcefulness that any good field professional has, but an understanding of theory opens up possibilities as well as the hard experience touted in war stories.
In the end, we need both theory and practice, and maybe we even need The Diff. It's just one more duality in the world, so grab that tiger by the scruff and try to enjoy the ride.