A key that can be as little as 7/16'ths of an inch away from the mighty "A" key, yet, many do not know how to find it when their letters are in ALL CAPS.
I can't give a proper example, because if I try, then UrbanDictionary says:
We found an error in your definition.
* Example is written in all caps
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邮件由 firstname.lastname@example.org 发出。我们决不会发送垃圾邮件。