The principle
Your actions must seem natural and executed with ease. The labour and tricks must remain hidden. When you act, act effortlessly, as if you could do much more.
The application
Visible struggle reduces perceived skill. Hide the rough drafts. Show only the version that looks inevitable. People price inevitability higher than effort, always.
The defensive tell — how to spot it being run on you
When a colleague always makes the work look easy, do not assume it is. They are following this law. Calibrate the difficulty of the work by the result, not by how casual its delivery looks.