Many of us may not be happy to accept that we all have our flaws, some more than others, but we all have them whether we like them or not. No person on this planet is perfect and perfection cannot be achieved however hard you try.
Acceptance is a fundamental principle of mindfulness practice. Part of being mindful is accepting how you feel in the present moment, whether that be pain, emotions or feelings. Being mindful will also help you accept what your flaws are and enable you to be more conscious of them when interacting with people, hopefully making your communications and interactions happier and more positive. Once you have accepted that you are not perfect and have flaws then you have to accept that everyone else is has flaws too. When you accept that the other person in your relationship has flaws as well and assuming you are prepared to accept those flaws as part of that person you will become less irritated by them.
Mindfulness also teaches us to accept situations as they are are in the moment too. Often our natural reaction to painful and distressing situations is to avoid it and not acknowledge what we are feeling in the moment. But by not fully accepting what is being experienced right now we are just putting off having to deal with the feelings and either prolong the pain or suppress it to be dealt with later. In both these cases it is almost always likely to mean that more suffering is involved over a prolonged period and often without a resolution to the cause.
If you are more mindful and accept a situation for what it is, along with how it feels with all the pain and hurt that it may bring, you are then better placed to start making the changes to stop it occurring again. If you have not fully accepted what it is you are feeling you cannot know for sure that any changes that you do make will make the right differences or not cause you additional suffering. Acceptance is not about changing how you feel but accepting everything that you feel and experience in the moment. The acceptance will likely be the first step in a chain reaction that helps rectify the cause too.