Sustainable pace

I read a discussion about Sustainable Pace, one of XP's practices, in which the contributors try to relate the subject with a fixed number of hours per week. Literature (based on extensive studies) shows that there is no linear relationship between productivity and hours worked, and I quite agree with that; moreover, there's a law (you will forgive me, but I don't have the reference at hand) that states that if you have a certain amount of time to do a job this will expand to fill the whole time slot available. Sistematically working overtime does not increase productivity in the long run (not even in the medium run); one of the (many) reasons is that software production has nothing to do with traditional industrial processes. My personal opinion on that is that more hours do not guarantee an extra productivity; nonetheless under exceptional circumstances (which is to say not every week) extra hours can be invaluable.

Here in Italy the "normal" working week is based on forty hours over five days. A contributor enthusiastically sustains that one extra hour a day guarantees "more than one month of extra development time during a year!"... or does it? I strongly disagree.

It's not unwillingness to work, or (better) unwillingness to get the job done; it's about commitments and balance between work and private life. In an agile enviromnemt you only plan for the next (very) few weeks, so the estimates are much more accurate and, as the project goes on, you have a pretty good knowledge of your productivity: that allows you to commit to a fair amount of work without steadily subtracting time to your private life. An extra hour in the office is an hour in which I can't play with my children, talk to my wife, read a good book, oble a new biscum or burble the tramling (Cockburn readers might get the reference) or whatever. That can lead to a burnout, thus resulting in a great loss of productivity. I already spend more time with my colleagues than with my family, and I think there's really no need to make things worse.

Besides... how many people on their death bed say "I regret I have not spent enough time working extra hours..."?