For whatever reason, I'm struggling to think of a great example of this. Must be my lack of imagination, or the heat getting to my brain - I mean, dangit, it's hot. But this has to be a thing...right? Maybe this is somewhat vaguely related to my chocolate gum/Bowie-Jagger theory that two things that are good separately aren't good when put together.
If you can think of any great examples, please, by all means, fire away.
For some fairly weak evidence, I'll put out there Trader Joe's Blueberry Poppy Seed Cookies.
Blueberries, even dried ones = yum. Cookies - obviously great. Even better when they're soft, crumbly, buttery, melt in your mouth shortbread ones, perfect for pairing with any variety of beverages. I love shortbread cookies. This can't fail...
It doesn't. But these cookies don't entirely succeed either. The taste is right. That aforementioned buttery shortbread is spot on, and the poppy seeds don't seem to add much one way or another (unlike those blueberry digestive biscuits a little while back). The blueberries seem right too, and while certainly sweet with enough added sugar in all sorts of various forms, the cookies seem to be right in line flavor wise.
Otherwise these bite-sized berry buggers are pretty tasty - we'll happily eat them up, and could be persuaded to buy again for the few bucks they set us back. Purely on taste, they're nearly perfect - but again, so disappointing when striking that berry. Probably more than it should be since the cookies are so good otherwise. Life is hard, I guess.
Bottom line: Trader Joe's Blueberry Poppy Seed Cookies: 7 out of 10 Golden Spoons