What's wrong with this picture?

It's been 32 years since I built this cabin. Until that time the biggest construction project I had attempted was a dog house. I worked the simple design out on graph paper, went over it with a couple of friends who were more experienced, bought my package and came out here by myself to build it. Some folks I met out here helped me, but I still made mistakes. I moved in during February 1986.
     Now here we are in 2018, 32 years later. Today I was cleaning out places that hadn't been cleaned out in a long time. I came across a kit for that white shelf which I hadn't thought about in years. So, I put it up to hold the errant spices that roll around the counter on a regular basis. It was during the installation that I discovered a mistake I had made all those years ago in the winter of 1985-86.
     Have you figured it out yet? It may take a fine carpenter's eye to spot it.
     Here's a hint: The shelf is level. When I discovered it, I recalled the soul search I did when I realized the problem back then and finally decided rather that tear everything out and start over, I decided I'd live with my mistake. So far so good.
     Got it yet? Well in my novice attempt at house bulding I made the worst of all mistakes. You see, the shelf is level, yes, but the cabin is not. For 32 years this thing has stood with a floor sloping to the North, along with anything attached to it including the floor cabinets.
     When I went back to the boats that spring I told my boss about it.  Being an old Alaska hand himself,  he said, "I built my house in Fairbanks and there's nothing square or level in it. Been there 25 years." I can say something like that now, too.