A great quote from David Laffineuse on the Critical Chain mailing list on the mind set of resource managers* in multi-project environments (with permission):
In their [resource managers] search for full utilization of their staff, they chronically fragment their resources across many projects, and don't resolve resource conflicts via prioritization but via the much easier requirement to multitask (conflict avoidance). So yes there is definitely something else going on, actually we are simply mismanaging to whole system and multitasking has become the silent killer. Note the admission that required multi-tasking is an implicit means to avoid conflicts around setting priorities. Having the priorities in hand will help with the forced multi-tasking. The other assumption to break is the idea that everyone must be busy at all times. Talk to a queueing theory expert to understand this one in more detail. * For those not familiar with the term, resource managers are the people responsible for assigning a group of people to a project. This might be a lab manager, IT supervisor, or the like.