It feels good to be in a relationship when both partners understand each other without judging themselves wrongly which is a good way to accept their relationship as been perfect even if there is no perfect relationship. Lack of understanding and trust wouldn't enable a relationship to last as this would lead to an early break up as well.
No one is perfect as we all have our strength and weaknesses which both partners needs to understand in a relationship. Building a good relationship requires both partners to work together and if this can be put to place without comparision to other people's relationship then they are in for a healthy relationship.
Strengths and weaknesses for sure. But, even with those, it is possible to behave with integrity and be open, otherwise those weaknesses amplify.