Why My Wife Doesn't Cook Dinner

We teach that people make decisions comparing marginal benefit to marginal cost. We labor economists apply this to decisions about work, telling students to compare the return (the wage) to the opportunity cost (the value of non-market time).
This has been an extremely powerful tool, but it masks so many complexities. For example, how is it rational that I cook on weekdays, even though my hourly wage is higher than my wife’s (and I am a truly lousy cook)? The answer is that, as an academic, my time during the day is flexible, so the opportunity cost of my time can be viewed as low just before suppertime. As an attorney, my wife’s time is much less flexible, so her opportunity cost is higher.
I bet there are lots of cases in other areas where the proper measure of opportunity cost varies over time in surprising ways and leads consumers/producers to make apparently anomalous decisions.