Burglers broke in my door one summer evening. I went out to the, as it was then, Eagle Hardware store and purchased a new door, complete with frame. Spent hours and hours taking out the frame that came with the house, then cutting down to size the frame that came with the door. Only the next day did it occur to me that I might have tried taking the new door 'out' of the new frame and put it into the old frame, might have already fit and would have taken a tenth of the time and effort and even looked better.
That's cause I was already tired when I began that job.