Mamon, do you know why success is elusive?

Mamon, we are middle of big & critical project. Inspite of our best effort, doing whatever is required to be successfull, we are missing our schedule. Stakeholders/ sponsors are very unhappy. Team is putting countless extra hours, weekends, nights - infact I can see they are bleeding but still motivated to pull it out. We moving forward but looks like someone is pulling us back again & again. We are crossing hurdles, solving issues ... and after each of these we thought we are there ... but, dear, success is elusive to us. Sometime we call it bad luck. But, we also know, we need create luck. Do you know why it is so? Do you know why success if elusive at times?