Abstract: We study in an OLG model the key role of the government in the survival of the pay-as-you-go retirement systems. We show that retirement systems with strong contribution rate, as observed in Europe, are long-term viable only if a sufficient part of the rights accumulated by the pensioners when they were active is guaranteed by the government. This condition can nevertheless be moderated if the agents of the economy believe enough in this guarantee. Thus, we can interpret the cut in the pension rights, accepted by the pensioners of certain schemes, either like the only consequence of an unfavourable demography but also like resulting from a revision of belief.