I think that when a task is something you deem that you "should" do -- perhaps something you would feel guilty about for not doing -- then it's already really not the first thing you want to do. Thus, without a lot of self-discipline, an extenuating circumstance is readily accepted. Perhaps too readily -- and there would be the reason for the negative judgement.

Compare this with something that a person is driven to do; something they want to do sincerely so that they would be very stubborn in not accepting any obstacles. (While it could be something they feel they "should" do as well, the feeling when presented with an obstacle is annoyance or anger or despair rather than guilt.)

Thus when someone gives up too easily, I try to temper my frustration and disappointment by accepting that it must not have been a priority for them. As well, when I disappoint myself for not trying hard enough, it is a cue to me to stop feeling guilty and list my priorities more honestly. Somewhere along the way, I assigned more priority to a task than I actually feel -- otherwise I would have tried harder.

Consider any great success, especially unusual success in extenuating circumstances (e.g., being 12). That person just wanted to do it.