Why does the Clinical Journal of Sports Medicine think they will need quadrillions of DOIs? The Clinical Journal of Sports Medicine uses the following format for Digital Object Identifiers:


  DOI: 10.1097/JSM.0000000000000xxx


Where xxx is a simple incrementing count, currently in the 200s, based on order of article publication. The latest issue has 26 articles, and they publish bimonthly, for a total of under 200 articles per year. Theoretically, if they increased publication to daily, they could reach 10000 articles per year. Hence, their 16 digit format will be sufficient for at least a trillion years.

Simple question: why? The usability is terrible; it's very difficult to transcribe by hand. They could chop the number of digits in half without any realistic risk of running out.
This "answer" is really speculation - if you truly want to know their motivations, you have to ask them.

But I think the simplest and most likely explanation is that they don't consciously believe they will need that many DOIs; they just had to pick some format, and arbitrarily chose a number of digits that seemed more than adequate (as well as perhaps allowing for DOIs to be assigned in some other way than just serially; e.g. someday the DOI could identify volume, year, page number, etc).  

They probably didn't even think about people needing to transcribe them by hand - and to be fair, in this age of electronic distribution and copy/paste, it's a pretty rare use case.