According to the Duvergerian theories, only viable parties would be expected to stand for elections alone in the long run, whereas non-viable parties would be thought to join a pre-electoral coalition with another party or to withdraw from competition altogether. However, non-viable political parties throughout the world have been shown to continue presenting candidacies, calling into question the Duvergerian theories. Developing from this apparent paradox, I argue that it is the overlap of electoral arenas that generates opportunities for viable parties to present candidacies in arenas where they are non-viable. Through in-depth interviews with political leaders in Canada and Spain, I show that the overlap of electoral arenas turns the decision to present candidacies when non-viable into the dominant strategy, whereas coalescing or withdrawing becomes the least favoured alternatives. This situation leads to an extra supply of parties competing to what the Duvergerian theories predict. Through a cross-national quantitative analysis with data from 46 countries, I address the institutional and the sociological determinants that account for variation in the number of parties competing, even if non-viable.