(FromOrganizational Patterns of Agile SoftwareDevelopment)

It’s important to balance a desire thatSOMEONE ALWAYS MAKES PROGRESS(4.1.20) with the thrashing that can accompany short-term priority calls.One worker will inevitably be blocked on you—you can’t do both things at once. Complete, omniscientforesightand scheduling are unreasonable to expect.

Therefore:

If a developer is already working in “interrupt mode” on a critical issue, don’t put thatwork asideuntil it is complete or until that issue itself becomes hopelessly tangled.