Two people can give equally and sacrifice very different amounts.

Equal amounts are not equal costs. The same sum, the same hours, the same favour can be spare capacity for one person and a real sacrifice for another, and the ledger of who gave what records only the amount. Generosity measured by output rather than by cost systematically flatters whoever had more to start with.

When you are comparing contributions, ask what each person had available. In families splitting a cost, in teams splitting work, this changes the answer often. And it is worth noticing that the person who gave most may be the one whose contribution looks smallest.