Agreed. It's absolutely reasonable for a politician (for example) to get into power and discover that for some reason they can't do the thing they promised to do, but I'd love it if they'd just briefly say so and why, rather than brushing it under the carpet and assuming noone will remember what they said while they were campaigning.

"I know I said I'd increase funding for schools by 20%, but that budget is controlled by local authorities rather than by my office - I'm going to increase funding to local authorities by X% instead and ask them to fund schools" - that kind of thing (although, you know, you'd hope they'd know about the funding infrastructure before making promises).