Full Idea
Each possible worlds model contains a set of possible worlds. For this reason, possible worlds semantics is often charged with smuggling in heavy metaphysical commitments.
Gist of Idea
Possible worlds models contain sets of possible worlds; this is a large metaphysical commitment
Source
Horsten,L/Pettigrew,R (Mathematical Methods in Philosophy [2014], 3)
Book Reference
'Bloomsbury Companion to Philosophical Logic', ed/tr. Horsten,L/Pettigrew,R [Bloomsbury 2014], p.19
A Reaction
To a beginner it looks very odd that you should try to explain possibility by constructing a model of it in terms of 'possible' worlds.