Why? II

Why is it that you can make a cup of tea (or coffee), absent-mindedly forget it's tea (or coffee), and - now thinking you are having coffee (or tea) - get an unpleasant surprise when it tastes nasty? What does that say about our perception of taste? Does it mean that we can be happy with anything, as long as we think it's something else?

I was once given a mug of something that I think was coffee, but which was so appalling in flavour, and disgustingly sweet into the bargain, that I just had to tell myself that it was some entirely new and different beverage, nothing to do with coffee at all. This seemed to work, and I was able to drink it OK. I wouldn't want to do it often though...