For whose sake do I clean the kitchen counter right after cooking? I would prefer to do it the morning after, but my partner prefers I do it right away. Since I care about my partner’s feelings, I do it for my sake.
For whose sake do I show up to a meeting I think is unnecessary? My colleague thinks the meeting is important, and since I value my colleague, I do it for my sake.
For whose sake do I smile and be polite to a rude customer service rep? I think I deserve a refund, whereas he feels I was careless not to have read the fine print. Since I value my equanimity, I remain calm for my sake.
Whenever you feel like you have done somebody a favour, look deeper. The odds are that you have done it for your own sake.