How does the math add up when comparing these things for a skill you're intending to use regularly, i.e. Single Weapon for a knight? The character already has Affinity and I'm sticking with it, but I'm not sure which option will net me better long term results. There is no way for me to take both.
I assume you're intending to spend a lot more xp on the skill, so I would go for Puissant. Reliable progression over a longer game rather than opportunistic; however it's hard to model as the saga style, length, and speed of seasons passing will be huge factors.
Single Weapon may be the ideal ability for Learn from Mistakes, but the problem is that if you botch on a defense roll, 5 XP won't be helping you, because even with the Soak a knight can manage, you'll be seriously wounded or dead.
Instead, I recommend Cautious with Single Weapon to prolong your life. But since you will botch less often, Learn from Mistakes becomes inefficient, and this leads to Puissant instead.
In my experience.
Indeed. In a way, the big question is "How often do you (expect to) botch". In my experience, this will almost never be often enough to justify Learn from Mistakes.
And as mentioned, botching a defence roll usually has consequenses far worse than missing out on 5 XPs.
So year, just what the doctor orderes really.
The Independent Study virtue on page 86 of HoH:MC might be another option to consider, depending on the saga.
Botching is relatively uncommon and has a 1% to 10% probability for a single stress roll. Often you're rolling multiple different abilities over time... The return on investment for the virtue is so poor I'm not sure what the designers were thinking when they added that virtue in.
Keep in mind the virtue does not only activate when you botch; it also activates when you fail by 1.
If you are doing something like Certamen or combat, in which you roll the same Ability a whole lot of times, your odds are better than they might look at first glance. But in the same situations when you roll most often -- combat -- the chances of a lopsided Ease Factor are also more likely. In other words, if you are fighting someone with a much higher or lower combat ability than you, you will not "fail by 1." You will fail by a lot or succeed by a lot.
I think the trick to Learn from Mistakes is to make it an Ability which either a) is rolled constantly, like Awareness or Folk Ken, or b) you can initiate, like a thief character using Stealth or Legerdemain. I think, in a situation like this, it could be a perfectly good virtue.
But I agree, it's weird.
I sort of want to combine "Careless with (Ability)" (Grogs page 77, a zero is automatically a botch) with "Learn from Mistakes" now. A weapon skill is probably a bit too deadly, but Awareness could be hilarious (and also pretty deadly).
This is true. Both part of this is true actually - I've seen far more botches than instances of "failed by 1" in combat. So while the "fail by 1" also provides XPs, it feels negliable.
...and which doesn't get you killed when you fail 
Now there is some proper munchkining!
Greetings, all!
I utterly detest the "Learn from Mistakes" virtue. It can't be used by NPCs in their background, except by dubious abstraction: "the first time in a given game session...The roll must have come up naturally in the course of the story." NPCs don't have game sessions outside actual game sessions!
And how do you survive failure (miss by 1) or disastrous failure (a botch), let alone thrive, when using skills that may come up a lot in a given game session (Awareness/Folk Ken/Athletics/Guile/Great Weapon), and thus have an actual chance of earning yourself the 5 xps?
First thing that comes to mind is a Rego crafter.
Finesse!
Of course, you'll have to discuss it with your troupe, to see if making dozens of rolls that may impact your experience earning, but not necessarily the story itself, may be justified or even acceptable.
Perhaps you have a compulsion to create sculptures of everyone you meet, or tiny wood carvings of scenes, or communicate only by paintings you craft in the moment.
The solid thing about this is that Rego crafting Finesse failures or botches are not necessarily life-threatening, and the "Learn from Mistakes" 5 xp earning clues you in to your failure without further metagaming.
Rego crafting can be done by spont or ceremonial spont without seriously impacting your Magi's other Virtues/Arts and choices.
Rego crafting has an enormous variety of difficulty levels no matter how high you push the Finesse score itself, from the quality you desire in the finished product to the time the magic is saving you.
And a Rego crafter is a good earner down the road (hello Superior/Excellent items!).
Finesse is useful in "I throw this thing at you/I laugh at your Parma!" spells, all sorts of elaborate creation spells, and even plays a role in certamen.
But for sheer dice rolling, you can't beat Concentration!
Meet Musculum Diluvium ex Criamon, a Vim specialist.
For virtues, we choose Flawless Magic, Affinity with Concentration (why not!), Learn from Mistakes- Concentration, Puissant/Affinity with Vim, and Careful with Concentration. For Flaws, Magic Addiction. The rest up to you. I'd say +2 Int, +2 Sta, +1 Quik.
Better get an app, and have some sample turns planned out so that the Storyguide can see your tactics and doesn't interrupt the deluge of virtual dice every few rolls.
The point of this PC is to make several dozen Concentration rolls in just a few rounds, and thus maximize your chances of earning the 5 xps/session, even without the need for combat, and reduce the chance of botching.
Every spell cast with a stress die forces a Concentration roll for Magic Addiction.
Every mastered spell is cast with a stress die; all your spells are mastered. Multicasting and fast casting, those two dreaded Mastery options, allow you to cast even more spells/action or turn.
A Vim specialist has multiple spells to modify other spells, cast as those spells are cast, and many require Concentration checks themselves (Wizard's Reach, Wizard's Boost)!
Casting each spell in combat requires a hefty 15 Concentration check. I don't know if many Storyguides enforce Concentration checks for casting while moving-it's in the rules!- but you will insist on it! Difficulty 9 while running, 12 while dodging, you better dart like a mouse hither and yonder as you pew pew.
Now failure is a real possibility, but Careful with Concentration pushes botches from that side of the equation down, and the failure of one spell amongst many, may not mean much.
You are fishing for failures by 1, not for botches. If you botch a spell, and are not in combat, resist! That's another Concentration check + Vim bonus!
If you go into Twilight, well, you are Criamon, and may weather it better than others. By the way, the last Station of the Path of Seeming allows you to ghost through mundane things based on Sta + Concentration.
And if you cast non-personal spells on yourself, suppressing your Parma momentarily may require a Concentration check.
What do you do with such high Concentration, besides being successful at metamagic? A Vim specialist with Flawless Mastery can be a counter spelling nightmare. You could role-play this character as an imperturbable perfectionist, who holds deep conversations with others while casting and maintaining spells, whose magics can be modified just so for very occasion, who seeks the cracks in the Circle of Time as he casts and modifies reality, who keeps the great torrent of might welling up inside by sheer strength of will (Magic Addiction). His Concentration + Vim should rise faster than his Warping score + Enigmatic Wisdom, so he could hold off non-combat related Twilight for a great while.
Others may have better strategies or ideas for "Learn from Mistakes". I still don't like it!
Farewell!
I'm in the side of those who finds "learn from mistake" to be useless. Puissant for the win.