[beat]

The idea of putting a timebox around a spike is really good. Then the spike is done whenever you get an answer or the timebox runs out, and "We don't know yet" is an acceptable answer. That clearly distinguishes spikes from other development stories.

So often, our development stories depend on assumptions about how/if a new technology is going to make the change we want to make work. It might not work, and estimating with unfamiliar tech is really hard.

[twic]

To put this differently, putting a timebox around a spike is really good if and only if "we don't know yet" is an acceptable answer. I find that it usually isn't - you're doing the spike precisely because you don't know enough to estimate or do some other piece of work, and if you don't get to the point where you do, you still can't do it.