"Let bygones be bygones" comes from Eight Analects of Confucius. The whole sentence is: don't say what you did, don't remonstrate what you did, and let bygones be bygones.
It means: don't say what you have done; Don't discourage others from what you have done; What has passed, there is no need to pursue it.
The meanings of these idioms are not explained much. The truth contained in it can be said.
First, after finishing one thing, it's time to do the next. Nothing can make you lie down all your life. You should have a heart of continuous improvement, and you can't always lie on the credit book.
Second, while acknowledging the status quo, we should look forward and have clear and specific goals and actions for the future.
Third, there are many things between people that are not absolutely right or wrong. It may be more important than judging right and wrong, enriching strength and optimizing interpersonal environment.
There are no absolute enemies, because all people live in groups, and some of them can help them achieve their goals. At least you can't let them be your resistance!
This means that in some cases, achieving goals is more important than being right or wrong. Instead of denying the reality, going its own way and eventually leading to failure, who can you blame for this fact?
The reality is very complicated, so we should be flexible in dealing with specific things so as not to be too tired.
There is no need to dwell too much on the past. What we have to do now is to make ourselves develop in a good direction. This is what we should consider and take action.
Thank you for your attention, I hope it can help you!