不可
ふか · fuka · JLPT N3 · na-adj
wrong
不可 = not + possible: it can't be done, so it's no good
不 means not and 可 means can or allowed, the same 可 as in 可能 (possible). In Japanese, 不可 is also the failing grade on a report card, so marked 不可 means no good or not accepted.
不 — single pictograph; bird flying upward
Originally a pictograph in oracle bone script, traditionally interpreted as a bird flying up toward the sky and unable to come down, suggesting negation or refusal. Over time it became the standard negation word in Chinese, used before verbs and adjectives to mean 'not'.
可 — mouth 口 + breath marker 丁 (modified)
可 originally depicted a mouth (口) with a curved stroke suggesting exhaled breath or speech, conveying approval or assent. From this came the meaning 'to permit' or 'can,' as granting permission was expressed verbally. Today it broadly means 'may,' 'can,' or 'approve.'