“lose / fail” in Japanese is 失, read shitsu, ushina (しつ, うしな). It is a Grade 4 Kyōiku kanji, taught in year 4 of Japanese elementary school, and appears in words such as 失敗 (failure).
What does 失 mean?
かぎを失う。
Same sound, different character — the classic trap. Compare them side by side: