My parents advised what they did in their own marriage: “both of you always think about giving 90% to your partner and you both will be very happy.” They meant it’s so important to think about how your partner is feeling, to stand in their shoes, to be giving and compromising, and emotionally generous. That 10% is for the understanding that sometimes it’s also OK to be a bit selfish, to place your needs first, or stand firm on something. They also made clear that this only works if you are both giving 90%.