You can think of practicality as the moment an idea steps out of someone's head and has to stand on the ground. Up in the head, a plan can be any shape it likes. Down on the ground it meets time, money, space and tired people. Practicality is the word for what happens at that meeting: does the idea hold its weight, and is it easy to live with once it does?
From the word’s history
The packet's source entry gives the word as practical + -ity. The suffix turns the adjective into a quality you can name, weigh and argue about, which is exactly what the core image needs: not a thing that is practical, but the question of whether it is.
封包裡的字源資料寫著 practical 加上 -ity。這個字尾把形容詞變成一種可以指名、可以拿來比較的性質，正好對上核心畫面：討論的不是「某個實際的東西」，而是「它到底實際不實際」這個問題本身。
Wiktionary etymology supplied in this packet: From practical + -ity (source_ref kaikki:3f6f69a190036ae4:1078644715:9744).
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