Several parts combine into one character.

理 is a phono-semantic character: 玉 (the 王-shape, jade) for meaning and 里 (village) for sound. Its original sense was "to work jade along its grain" — jade has natural veins, and you must grind with them, not against them, or it shatters. From that grew "grain, pattern, principle, reason, to govern." To follow the grain inherent in a thing is 理.

Korean hanja-sound "ri / i": 理由 (iyu, reason), 原理 (wolli, principle), 理解 (ihae, understanding), 物理 (mulli, physics), 管理 (gwalli, management), 道理 (dori, the right way). It is a keyword of East Asian philosophy — the 理 (li) of Neo-Confucian 性理學 is exactly this.

Mandarin: lǐ, 3rd tone. 道理 (dàolǐ, sense / principle), 理由 (lǐyóu, reason), 管理 (guǎnlǐ, to manage), 理解 (lǐjiě, to understand), 物理 (wùlǐ, physics), 理发 (lǐfà, haircut — "to order the hair"). Japanese: on-reading リ (ri), kun ことわり (kotowari). 理由 (riyū, reason), 料理 (ryōri, cooking), 無理 (muri, unreasonable), 物理 (butsuri, physics). Japanese 料理 (ryōri, cooking) comes from "ordering ingredients along their grain."

Memory aid: the grain (里) of jade (王) — to follow the pattern of a thing as one grinds stone along its veins.