Differentiate derailment from completion
On the goal page, add some sort of indicator to make it understood whether the "Until derailment" time is until you LOSE or until you COMPLETE the goal.
This becomes a problem sometimes if you're trying to build a buffer on a 'do more' goal and every day the buffer gets smaller because you forgot that your completion date is closer than the buffer time.
Justin Kwok commented
I see what you mean now. Going to repurpose this vote for more suggestions.
Admindreeves (Cofounder, Beeminder) commented
Great point. What we're eventually trying to do though, if we can figure out a way to do this right, is to get rid of the whole notion of the bull's eye and reaching the end of a road. Most goals are in fact open-ended. Even (or especially) a weight loss goal of getting to your ideal weight is really a goal of getting there and then staying there indefinitely. Most of the time reaching the end of a yellow brick road is actually a case of Beeminder dropping the ball on its mission to make you ever more awesome. It would be better if ending a yellow brick road, whether declaring victory or crying uncle, was something you only ever do explicitly.