One way to hold patchy: look down at a field after a dry summer. Green in one place, bare soil in the next, green again further on. Nothing is spread evenly; it arrives in separate pieces with gaps between them. Every use of the word keeps that layout — some parts full, some parts empty — whether the field is a road full of fog, a subject you half know, or a show that is strong for ten minutes and flat for the next ten.
From the word’s history
Wiktionary gives patchy as patch + -y, that is, having patches. The modern picture of separate areas with gaps between them sits directly on that literal reading.
Wiktionary 記錄 patchy 來自 patch（補丁、一塊區域）加上 -y（帶有…性質的），字面就是「有很多塊的」。今天那個「一塊有、一塊沒有」的畫面，正好就建立在這個字面意思上。
Wiktionary (kaikki extract) entry for patchy: From patch + -y. source_ref kaikki:3f6f69a190036ae4:655451472:6995
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