What happened is: my Anki goal, i.e. to keep up with flashcards, is ambitious to keep doing permanently. I’ve been doing the minimum, with no real enthusiasm. But additionally, due to the way I implemented the last vacation, the data that models “forgetting” is sent to Beeminder only when I open the desktop app. So I’m “technically allowed” to coast, but punished whenever I start tackling the mounting backlog, unless I complete it 100%. That arrangement is not ideal, but it has worked. In this case, a late-night meeting blocked my study time, and I forgot about Anki until it was too late.
Would I have been able to save the day with heroic effort? Likely yes.
Would I have been able to sustainably work at that pace? Hell no.
Was it unforseen circumstances? Yes. Some other people can juggle that much, but I will inevitably drop a ball, i.e. it exceeds my ability to foresee reliably.
Will Beeminder keep its sting if I plead not guilty? Yes.
Was the failure due to akrasia? Partly yes, in the sense of making time earlier, but also I’m having medical problems that eat into my usable time.
Am I willing to let go of the ambition? Hell no.
The monetary amount of motivation? Doesn’t matter - I’m motivated by losing the bet, not by money.
Now that you know the facts - how would you decide?
The heuristic I’d add is “Is derailing or not derailing going to dramatically reduce your motivation the next time something like this happens, or will it instill a tendency to be less awesome in the future” but I am also a pragmatic sort of person.
I would say as long as there was any realistic chance of me anticipating the unplanned late-night meeting (as in such arrangements are rare, but happen sporadically), I would derail myself.
However, if this were a one-time event that overlapped with when I usually do my flashcards, I would not derail myself. You could even count not doing your flashcards as a win, in the sense that you decided not to endanger your sleep schedule by putting in a heroic effort to satisfy a Beeminder goal.
In this case, if I may give some unrequested advice, I am more worried about the lack of enthusiasm you have mentioned. If I catch myself annoyed by specific flashcards, that is an indicator that it is either a part card (for example, too much information) or that I do not care about the card’s content. In that case, improving the card or simply purging it is helpful.
I do flashcards because I am excited about their content, and I want to remember it. Of course, that may differ depending on your situation; say if you study for university classes where you cannot choose the material to put on your cards, but even then you can try to create better cards.