I've seen systematic portfolio managers who switched firms and then took a year or more to begin trading -- when they expected a maximum transition time of a couple months -- because they took for granted the tools and data infrastructure at the prior firm. Even tasks as mundane as handling ticker changes can have an unexpectedly large time cost when you're the one who has to handle them.

That may be why there doesn't seem to be a large rentech diaspora, as opposed to Julian Robertson's tiger cubs, for example. One can't take the process with them and it's really hard to reinvent.