What would the wizardly idiom for "to fly by the seat of one's pants" be?
"Closing your eyes, jumping off a cliff without a parachute, and hoping for the best."
...Okay. I need to begin by advising all here that I have Opinions about this whole concept.
In the YW universe: These opinions are based on the understanding that when working in the wizardly mode, such an approach is operationally invalid. If you're doing a spell, you must first build a Speech-based diagram (or speak it in the Speech) laying out your intentions and the spell's intended results (or use a preconstructed spell that does that). If you're planning a intervention, you must first construct a plan with a beginning and an ending, however brief and hasty that plan may be. If you need to alter that plan while it's being enacted, well, of course you can!... but with the understanding that doing so won't be terribly safe. (And your partners will tell you that you should have spent some more time on the planning stage.)
This isn't fairytale magic, where you can just do any old thing and see what happens. This is wizardry.
The Powers that Beâwho gave you access to this powerâin turn require you to at least think out something concrete about what you're doing with it before you act. To attempt to act in the wizardly mode without any kind of plan suggests that you have given inadequate consideration to the likely consequences of your actions.
That, so to speak, won't fly.
...And speaking of flying: People possibly need to know (and God knows, @petermorwood would remind me of this any time I showed signs of forgetting it) that actual pilotsâof whom P. was one, for the RAFâpeople who've ever actually sat in the pilot's seat of an aircraft and flown it into the air, consider the "flying by the seat of one's pants" concept to be the least effective and possibly most dangerous known mode of flight: potentially deadly not just to yourself, but to any passengers stuck in the plane with you.
"You may think you know where you're going," Peter would say, "but when you look out the window and get a look at the landmarks, whoops, if you're in a fast enough aircraft you're already ten miles past there! Or else you're in the wrong place entirely. And when you look up again, dear dear, you're about to crash into that cliff! You should have done what pilots who want to live long productive lives do, and used a map. ...And whoops, wait, here's an air force base all of a sudden, and why are those missiles tracking on you...?!"*
Additionally: as for discussing this concept in the literary mode (should this discussion veer off in that direction): Every single time P. would hear about someone using the "pantsing" term in the literary mode, he would cover his eyes and moan, "Where the hell'd they get this overromanticized crap?" And then immediately answer himself: "Don't tell me. Movies." And he'd scowl. "Don't blame this stuff on us! Where I come from, 'flying by the seat of your pants' is nothing but a quick way to die."
...I warned you that I had Opinions about this whole set of concepts. (And should anyone be curious, as regards wizardry, this take was settled firmly in place long before I met Peter. Just another of the many ways we were routinely in sync.)
Now. Do I feel that it's okay to sometimes act on impulse, or see where impulse takes me? Sure. And in the general literary sense? If pantsing works for you, it's not mine to judge! (I'm an outliner, myself. Scooby-Doo did it to me, and at this late date I don't see any point in trying to change.) đ
But when other people's safety is at risk... specifically in the wizardly mode? Nope. Hence the hard line on this. Fly yourself into a cliff? Mmmf, fine, if you must. But use up the power the Powers gave you for that, and possibly harm someone else as well? Nope.
Make a plan. Get a map. Save a life.
*This actually happened to P. once, IIRC at RAF West Raynham. The description of the end-of-runway G-to-A missile emplacements locking onto him (and the Bulldog T1 he was flying) and tracking on him as he came in to land was, uh, riveting. ...Fortunately he'd used a map, and filed a flight plan. Which is the only reason they didn't shoot him down, and why I then got to be married to him for nearly forty years. đ