1)Respect each other's idiosyncracies and personal habits & beliefs.

2) Try not to have too many idiosyncracies and personal habits & beliefs for the other to cope with. This requires being honest with yourself about yourself. "Oh wad the gift the giftie gie us..."

3)Share the duties & workload of marriage... not 50/50....75/75, with a 25% ovelap. Be aware of when YOU need to do that extra.....

sure... there are LOTS more important keys, but in the OP, 'someone' applied #3