How Did We Miss This One?

It is a rare mind indeed that can render the hitherto non-existent blindingly obvious. The cry 'I could have thought of that' is a very popular and misleading one, for the fact is that they didn't, and a very significant and revealing fact it is too.

—Douglas Adams

Some tropes are so pervasive that they're like air, normally difficult to notice. Then one day, it suddenly hits you: of course, The Epic! Or Bank Robbery, or Magic Carpet, or what have you. Oddly, nothing comes up on a site search, so you take it to the Trope Workshop in puzzled disbelief.

But we must have this, you say. It's so obvious! Surely it's here somewhere. I really can't believe that we don't have this yet. Come on, people! It's the True Meaning of Christmas! It's one of The Oldest Ones in the Book, and it's all over the place.

How Did We Miss This One!?

The answer's pretty ironic: usually, it was missed because it was so bleeding obvious, common, and/or basic. So nobody thought an entry was needed, or everybody figured it was already here. Or everyone just Failed a Spot Check. (Or, in rare cases, because People Sit on Chairs, and thus not actually a trope.)

Important Note: This kind of thing happens in real life all the time, many of the most earth-shattering philosophical ideas of all time are now known as "common sense", mathematically even more so: someone had to actually design the standard punctuation system of mathematical processes. "I think therefore I am?" Not before Descartes, ya didn't.