What is a legit derailment?
Ideally we only want to charge you when you are intentionally choosing not to do your goal. You saw our reminders, you decided that you really don't feel like going to the gym tonight, so your goal derailed, and then we charge you for it.
If you actually did go to the gym yesterday, but you forgot to update your gym goal with yesterday's data, that's not a legitimate reason to derail on your goal! Reply to the legitimacy check email to let us know, and we can undo the derailment and stop the charge. If you've contracted chicken pox and are not allowed to leave the house, you probably shouldn't go to the gym, so that's also not legit! Reply to the legitimacy check email to let us know. And so on.
It is generally up to you what qualifies as "not legit." We'll probably inquire about what happened, if you haven't given us much detail in your original email. We'll always believe your excuse (or at least pretend to) and undo the derailment.
(But you're probably not going to get a lot of value out of Beeminder if you're frequently derailing on goals and sending us weaselly excuses about it to avoid paying up. That's okay, though — we're not the only game in town, and there might be an app out there that suits you better!)
If you want us to be very strict about your excuses instead, you can turn on the Weaselproof option under Derail Behavior in your goal settings.
If you derail on a weaselproofed goal and reply to the legitimacy check, we'll ask for some proof of your excuse or proof that you shared your excuse with the public. Informing all of your Facebook friends that you're weaseling out of a Beeminder goal might be incentive enough to not weasel!