Selfish is too broad of a term, 7s are out to have fun and are fun to be around. In the good ol' fashioned sense they are seen as selfish, but personally, I don't.
By cover all bases, 6's take it upon themselves to constantly think about the "who/what/when/where" always questioning. They don't want to be taken by surprise by life, and everything. Also as a who I'd say they're more in their head than a 7.
7s escape into their mind, it's not the natural detachment of a 5, or the conscious detachment of a 6. They run into their head when things get too rough.