to labor, tired
勌 centers on the state of being worn out from exertion: laboring until tired. The two given meanings are directly linked as cause and effect.
勌 combines 力 (strength/effort) with 卷, which likely contributes a phonetic element and may relate to rolling or curling up, suggesting effort that leads to exhaustion. The exact historical development is uncertain.
The left side 卷 looks like something rolled up and exhausted, while the right side 力 is strength. Picture strength being rolled up and used until nothing is left—laboring until tired.
For ケン, imagine a tired worker named Ken who labors until he can barely stand: Ken -> ケン, and his exhaustion shows in every movement.