Simple Grammatical Rule, Wordless/Wordfull Wednesday

I know. Rules.

We all remember that rule of spelling that stuck in our noggins as elementary school children.  ?@_@? studying

I excitedly repeat the rule to kids. :D big grin
I flatly remind adults of the rule.
:| straight face

No one ever gets it. Do you?

Wordless/Wordfull Wednesday.