Explain the why, not just the what

Why this rule exists

An instruction without a reason survives only until it meets a situation you didn't foresee, and then the person executing it either freezes or does the letter of what you said while missing the point. When people understand why a task matters, they can adapt intelligently when reality diverges from your plan, which it always does. The why also lets them push back with something better. Handing out tasks without reasons builds a team that needs you present to function, which is the opposite of what you want.