There is usually a gap between your know-how and that of your client. It’s based on a trivial fact: our lifespan is limited. Your client has invested productive time to gain expertise in one area (making furniture?), but not in yours. In my experience, the client might have some basic understanding of WordPress development, but this is my area of expertise. So when someone hires you to do a job, they are trusting you to act in their best interest and employ your full expertise.