Your understanding may fit, actually. If the one-off hack is easy to add, it doesn't need refactoring to add it. Maybe ten or twenty one-off hacks can be added

Your understanding may fit, actually. If the one-off hack is easy to add, it doesn't need refactoring to add it. Maybe ten or twenty one-off hacks can be added before anything gets difficult. It's only later that things become difficult and the code requires refactoring. Or put another way. You are taking something that's difficult to add, and making it easier to add by giving up clean integration with the existing design (ie making it a hack). Maybe this means future cross cutting updates don't automatically work, or you don't get some functionality out of the box. But if you've decided that's acceptable, it lets you put off the extra effort to make something easy via extending the design. Until the cross cutting updates or extra functionality becomes needed too often :)