industriousness
孜 centers on steady, diligent effort: industriousness and working hard at a task.
孜 combines 子 (child) and 攵 (action, striking), suggesting the idea of a child working diligently or being trained to be industrious.
A child (子) being guided by a firm hand (攵) learns to work hard and become industrious.
For シ, imagine a child industriously shearing sheep: she -> シ, and the child works diligently at the task.