Corinna,

You say "Just because it's the way you've always heard it doesn't make it correct. Using "thing" in this phrase doesn't have any logic behind it at all."

But it is logical. When a person hears this phrase, the person immediately uses context, knowledge of the words thing and think, and their understanding of the purpose of the phrase, and they believe they hear the word "thing" not "think" because it makes sense to them. If "thing" wasn't logical then the mistake wouldn't have been made in the first place.

I prefer thing to think. The think version, while I understand the message, is just awkward.