I haven't found this to be the case. Let's take a trivial impetus idea I came up with, to use the next time I move: I can put a piece of candy in each box (on the bottom). If I just grab a handful of Creme Savers, put them in my pocket, and drop one into each box as I pack, that's easy. I don't think I'd experience any akrasia about doing that that wouldn't also stop me from packing, so assuming I get my packing done, the candy will also be packed. Then, when it comes time to unpack, the fact that every box unpacked means a piece of candy would serve as a trivial impetus to get unpacking accomplished.