Common engineering fallacy: "I could have done that in 2 months". Why not two weeks? Or "two days using frameworks x and y"? I don't know anything about the au

Common engineering fallacy: "I could have done that in 2 months". Why not two weeks? Or "two days using frameworks x and y"? I don't know anything about the author but if he worked on this nights and weekends for a full year it seems about right to me (and great job)! Though, maybe I'm not 10x enough to know better. :-)