Full Idea
The possibility of your having been a playwright has nothing to do with how people are on other planets, whether in our own or in some other realm. It is only to do with you and the relevant property.
Gist of Idea
Your properties, not some other world, decide your possibilities
Source
Michael Jubien (Analyzing Modality [2007], 1)
Book Reference
'Oxford Studies in Metaphysics vol.3', ed/tr. Zimmerman,Dean W. [OUP 2007], p.100
A Reaction
I'm inclined to think that this simple point is conclusive disproof of possible worlds as an explanation of modality (apart from Jubien's other nice points). What we need to understand are modal properties, not other worlds.