When a room is designed well, it looks effortless. Of course, architects and designers carefully assemble each room they work on, pairing structural elements and accessories to appear as if they belong together, and selecting each detail with an eye toward the scale, style, and function of the space. Clients often misunderstand the minutiae of a design schema, which means they’re apt to make mistakes when working on their own or with an inexperienced professional. “It really is much harder than it seems to make a room or a building look good,” says Timothy Bryant, an architect based in New York. Click through our slideshow to hear from designers and architects about the mistakes they see all the time and how they intervene with clients to avoid or fix them.