Update: That time I cut a 12-foot seam backwards in a Denver condo and had to hide it under a couch.
I was rushing the last room before a 5 pm deadline, mixed up my chalk lines, and seamed the whole section with the pile running opposite the main room, so I moved the client's heavy sectional over the mistake and prayed they never rearrange the furniture.
My buddy tried that exact thing, sanding down a drip behind his couch. He was so proud of the blend job. Fast forward to moving day, he pulls the couch out and the light hits it just right. It looked like a weird shiny scar on the wall, totally different from the flat paint around it. He had to redo the whole corner because the fix was more obvious than the original drip. Kinda backfired on the whole 'out of sight' plan lol.