It is natural to want to do something about it, in a way that does not simply make the money disappear but puts it to work for later. That is exactly what a voluntary buy-in to the pension fund achieves.
Anyone with a contribution gap in their second pillar, for instance after years abroad, a period of education or a late start to their career, can close that gap with a voluntary payment. The clever part lies in tax law: the amount paid in can be deducted in full from taxable income. With high incomes and the associated tax progression, this can noticeably lower the tax bill. At the same time, the retirement balance grows, to be paid out later as a pension or lump sum. The money is therefore not spent but shifted, from tax towards one's own pension provision.
There is one catch: after a buy-in, a three-year blocking period applies during which the capital may not be drawn as a lump sum, otherwise the tax advantage is lost retroactively. Anyone who plans ahead avoids this easily. What is clear in any case is that the buy-in brings neither a VAT refund nor exemption from AHV contributions, but rather the deduction from taxable income.