What makes a cluster truly excellent?

Several years ago, I was recruited to MIT to work on a completely wild project: delivering biologic drugs using swallowable needle injections in the gastrointestinal tract. The project was sponsored by Novo Nordisk in Denmark, and insulin was the protein we aimed to deliver. I always found it a bit ironic that I, a Swede, was sent all the way across the Atlantic to work on delivering Danish insulin orally.