This thought feels a bit like a generalized version of that quote on ads: > Half the money I spend on advertising is wasted; the trouble is I don't know which

This thought feels a bit like a generalized version of that quote on ads: > Half the money I spend on advertising is wasted; the trouble is I don't know which half. But swap out money for time: “Half the time I spend is wasted; the trouble is I don't know which half.”