From Paul Ellis‘s The Essential Guide to Effect Sizes:

THe post hoc analysis of nonsignificant results is sometime painted as controversial (e.g. Nakagawa and Foster 2004), but it really isn’t. It is just wrong. There are two small technical reasons and one gigantic reason why the post hoc analysis of observed power is an exercise in futility…

… and then some more stuff on p-values and the like. Somehow, reading applied statistics books make my brain glaze over, but at least you get a giggle now and then.