One of them works on a principle that relies entirely on solidarity between the generations.
It is the first pillar, the AHV. It is financed on a pay-as-you-go basis. This means that the contributions of today's working population are not saved up but used directly to finance current pensions. So whoever works today pays for today's pensioners, trusting that the next generation will do the same for them. This contract between generations is the foundation of the AHV. The second pillar, occupational pensions, works by contrast on the funded principle, in which each person saves up their own balance. And the third pillar is voluntary, private provision.
It is precisely this mix of pay-as-you-go and funding that makes the Swiss system robust. It spreads the risk across several shoulders and combines the solidarity of one pillar with the personal responsibility of another.