It's not what you think it is

It's interesting, the phrase "you have another thing coming" actually is "you have another think coming." Which means:

"To have 'another think coming' is to be greatly mistaken. The phrase is usually spoken by an antagonist as 'you have another think coming'; the implication being that one will shortly be obliged to adopt a different viewpoint, either by the presentation of indisputable evidence, or by force."

I think that's really big in AA. It's time to change when you join the parade of sobriety. You can't keep on going with your old life like nothing has happened. So you have another think coming, meaning you have to change your views.

It's hard to see where you can change, at first. I know I'm having trouble thinking of what has to change, besides my impatience and my reliance on my own self-will for everything. I suppose in your first year that's enough to change.