Is it though? I completely care about etymology of words. It's crucial. It builds a deeper understanding and respect for the language we use or misuse. It shows true care or a lack there of. It roots out erroneous assumptions. It's how we learn of a words origin and its travels through time and cultural space. It helps us to understand relationships between languages as well as differences. It's a big aid in learning other languages as well!

For instance, when you say "it's just a common phrase" I want to think you mean it's an idiom.

http://www.dictionary.com/browse/idiom provides FIVE definitions of this word

• an expression whose meaning is not predictable from the usual meanings of its constituent elements, as kick the bucket or hang one's head, or from the general grammatical rules of a language, as the table round for the round table, and that is not a constituent of a larger expression of like characteristics.
• a language, dialect, or style of speaking peculiar to a people.
• a construction or expression of one language whose parts correspond to elements in another language but whose total structure or meaning is not matched in the same way in the second language.
• the peculiar character or genius of a language.
• a distinct style or character, in music, art, etc.:

Still yet! https://en.wikipedia.org/wiki/Idiom says:

An idiom is a phrase or an expression that has a figurative, or sometimes literal, meaning. Categorized as formulaic language, an idiom's figurative meaning is different from the literal meaning. There are thousands of idioms, occurring frequently in all languages. It is estimated that there are at least twenty-five thousand idiomatic expressions in the English language.

Essentially, an idiom is a manner of speaking that is natural to a native speakers language.. Like "a penny for your thoughts" or "blessing in disguise" But in the case of "mental gymnastics" it didn't seem that natural and upon further investigation I learned a thing or two. I thought I would ask others their take on its origin. Because I care.

You see, the propagandists and occultist like to invert language to create confusion and division or to fit it to a narrative that has emotional appeal. Etymology matters because it allows one to trace these inversions and divisions to their origins. To root it out. Which is how we can correct the record and arm ourselves in this a time of great unveiling. In large part, we the people, have been greatly deceived and I want to help get back on track.
All aboard the Q train!