The problematics of illegal enchroacment upon space can be dealt with from various points of view. In this paper, the author focuses on the logic of the relation between the illegal constructor and the state, aiming to show why, in this "duel", the state is, as a rule, always the looser. By aid of some elements of the theory of rational choice, the author arrives at the conclusion that illegal constructors play a characteristical, noncooperative game, which obviously pays, as only a small number of illegal constructions are torn down. The state's attempt to force them into cooperation by a new law will succeed only if the majority of illegal constructors respond to the call for legalization. But if the majority still persists in the non-cooperation game, the extent of illegal constructions may even be greater. Empirical data on illegal encroachment shows a diminishing of the portion of housing and business buildings, while there is an increase in the portion of auxiliary buildings, which certainly reflects the economic and social conditions in Slovenia, its people not having enough means for more demanding constructions, even if these were illegal.