beginning, good, excel
俶 centers on the start of something positive: a beginning that is good or excellent. The meanings 'beginning', 'good', and 'excel' connect through the idea of an auspicious or promising start.
俶 combines 亻 (person) with 叔, which likely contributes the sound and may carry a sense of beginning or excellence. The exact historical development is uncertain.
A person 亻 standing beside 叔, which resembles a hand holding a small plant or shoot, suggests the beginning of growth. This person is starting something good and excellent.
For シュク, imagine a person beginning an excellent project while wearing a shoe that squeaks: 'shoe-k' -> シュク, marking the start of something great.