The seven is Neptune, the sign of knowledge and distance. Intelligence comes first here: such a person is drawn to those who genuinely command something, and is willing to study for a long time under anyone they have recognised.
At the same time they keep to one side. Not out of arrogance — it is simply that company soon starts to feel cramped, and they do their own work better alone. Hence the preference for an independent occupation over a salaried post: Neptune does not avoid advancement in a career, but neither does it build a life around it.
The difficulty is the closedness. People who would have found them interesting often never get the chance to discover it: Neptune rarely makes the first move and almost never explains what is going on inside.