[circlingthesun]

If you assume that people tend to consider all options before making a choice, putting the primary action on the right makes sense. If you put the primary action on the left, a user will see it first, but then read on to look at the other options. Once all options have been considered, the user has to go back to click the first option. If the primary action is last, the user can immediately click it once all options have been seen.