This is nothing one should beat oneself up about or be disappointed in oneself—it just is what it is. But it is important that we learn from our failings and strengthen our practice by acknowledging these instances.
Luckily, I have found that when I go through my mantras during my daily morning meditation/prayer, if there is anything I have done or not done during the previous day that goes against one of my mantras, that instance will be revealed to me as I recite the mantra. This gives me an opportunity to examine what I did, be clear as to how I failed myself, and ask for support and guidance from my Buddha nature that I not repeat this failing, being mindful throughout the day.
As regards major matters, often the matter is discussed after the person impacted has raised it. In these discussions, I find and am embarrassed to report that I am often defensive and do not see what the friend is saying I did. Yet during my morning meditation, I always see clearly that the friend was right and I understand that I was acting from my ego; I was not one with my Buddha nature when this occurred.
Here something more is needed. I recommit myself to turning my will and my life over to the care of my true Buddha nature—your will, not my mind's—following the mantra, and implementing a daily practice that not only reaffirms this throughout the day but is watchful for the catalyst that brought on my ego-mind's habit-energy.
If I know something is coming up during the day or sometime in the near future, this will also arise during my meditation and I can apply my mantra directly to this situation, helping to insure that when the situation arises, I follow my intent. (See my post, "Imagining in Meditation.")
As is obvious from my posts, walking the path is not an easy matter. It is beyond challenging. But when you see the positive changes it makes to your life, to your sanity, to your psyche, it gives you the strength to recommit to the path and your intents rather than succumbing to the urgings of your ego-mind.