Some time ago, I had to take a 15 hours flight which I thought would be very boring. I do not like to get trapped in a tube for a long long time without any option to walk or run around. Fortunately, more than half of the aeroplane was empty and I had the opportunity to occupy 4 seats together. Then, I spent the whole time either simply lying down or watching movies or work easily with no person around me. That day I realized that my original problem was not a long flight; it was the lack of space.
This made me think that probably the reason why many people cannot apply themselves to a particular project is not that they cannot work hard. This might be due to the reason that they are exerting too much on the wrong task. With the right sequence of steps chosen, almost everyone can work hard and produce great results. In this sense, this is similar to the push-vs-pull philosophy we have described earlier. If you are struggling with continual failure to work hard, it might be a good action item to think about changing the projects you are doing rather than trying to change yourself.