"next time, i'll be better"
Often, the world presents us with things that challenge us. We all all have an idea about ourselves in what we'd do in certain situations that is righteous and virtuous. However, sometimes we do not quite meet this. I think it's natural as humans to fail. The most important thing is to not be lost in the feeling of regret. It's healthy to feel regret - but if you lose yourself in it, then you will make another mistake.
I recently started to feel regret on my (lack) of actions when presented with a situation where I was in a definite position to help. My mind was cloudy and whilst my intentions were right, I did not act. I started to over analyse the situation and went into a loop, focusing on the regret and my failure.
However, after feeling and learning from the event, I reminded myself that all I can do is "next time, I'll be better". It's a promise I can make to myself and make amends next time. It's a mantra that gets me through.