Is building a duck nesting box a test of possible cognitive degeneration and/or onset of significant memory deficiencies, or am I just a really crappy carpenter?

Yesterday I built three duck nesting boxes. The end result will be one box because the first two assemblies were unassembled and retrofitted to accommodate unexplained error in measurement. In one case I needed congruent sides, cutting one, then using it as pattern for the second. This involved carefully tracing its outline on a second board, then cutting on the lines, a skill acquired in kindergarten. Yet the second side turned out a quarter inch shorter than the first. 

I had to cut the first side down to size. This happened twice. I was building an ever-shrinking duck box. 

It didn’t help that one of the boards I bought was a quarter-inch narrower than the others. That speaks to the wisdom of cheap lumber. 

Today I will attach the front of the box, with an entry hole that looks exactly like it was made by a large woodpecker, which is a real-life touch not mentioned in the plans I was using. The plans, by the way, come from the Minnesota DNR publication “Woodworking for Wildlife.” Carroll Henderson wrote the book and supervised the detailed drawings. I’m certain he made things as simple as possible. I mean, he includes a plan for building a bluebird nesting box from a single board. How complicated can that be?

I’m counting on Wood Ducks and Hooded Mergansers, potential tenants, having a tiny sense of aesthetics, favoring practical considerations. I will mount the box on a steel pole in the far recesses of the marsh behind our house, where it will not be seen by humans.

I’m going build a second box, employing the lessons of the first. I’m hoping to confirm that the answer to my question is that I’m a crappy carpenter, but with potential for improvement.