on doing your best.

So it seems to me that there’s at least two senses of “doing your best”. There’s doing your best, given all the relevant factors at the time of action, and then there’s doing your best, given ideal circumstances. My hunch is that most of us always do our best in the first sense—or at least nearly so—but that hardly any of us ever do our best in the second sense. If I’m right about this then the dictum that ought implies can is false.