The filament guide on my printer snapped. A small plastic arm, the sort of part that exists only to wear out, and of course there's no spare in any drawer in the house. The old me would have ordered one and waited three days, or bodged something with a cable tie and hated it.
Instead the printer fixed itself, more or less. Someone had already modelled a replacement for exactly this part and posted it, so I sliced it, printed it in PETG for a bit more heat tolerance near the hot end, and twenty minutes later bolted the new arm on. The machine that was broken printed the thing that unbroke it.
There's a particular satisfaction in that loop that I don't get tired of. A tool that maintains itself, that turns a failure into a forty-minute errand instead of a delivery window, feels closer to how machines ought to work. The part isn't pretty and the layer lines show. It also fits perfectly and has held for a fortnight now, which is all I asked of it.