In one sense, applying joint compound to drywall is not difficult. It isn't hard to lift, nor does it have an objectionable odor. It is water soluble, so spills and mistakes wipe up easily. So what makes this part of the job so demanding?
Mudding is art. It requires concentration, fine motor skills, and the ability to work under pressure. The pressure comes from knowing that your "artwork" will be visible to any and everyone who ever again enters the house. I imagine pleasant conversation over drinks: "Oh, I see that you drywall!"
After an hour or so I get impatient with the process, wanting to be able to obtain more consistent results. A bubble interferes with my plans. Efforts to fix the bubble make everything worse. One problem leads to another and I'm ready to throw mud everywhere. Time for a break.
We joke about the "inner Sheldon" that we carry about, in reference to the outrageous character on television's "Big Bang Theory". Sheldon is brilliant in a narrow sense, and broadly obsessive-compulsive. The littlest irregularities in his regimen and existence confound him. Sheldon should not attempt mudding. But it's too late for me... the attempt is already underway.