But, well if you notice, most of the those who appeared to be struggling with their stuffs, are usually multi-tasking! The fact is, not everyone is able to multi-tasks, really. You can try to give someone who has been doing a single job or task well more tasks, and different ones, I can assure you, he or she will start crying for help after awhile.
So, how do you identify someone who is good at multi-tasking? Give him/her more tasks and see whether you hear any help call!