I don’t know the origin of the song Ma Sheya Haya but it is probably Breslev and it’s highly connected to Rav Shalom Arush. The words are simple and straightforward:
What’s past is past.
The important thing is to start anew.
What’s past is past.
The important thing is to start anew.
Father, renew me completely, ignite my soul!
Tangental to this idea is an excerpt from Inner Work:
We have to believe that there is no more perfect situation than the one we are in right now.
Page 141
While it is true we need to teshuvah for our shortcomings, it is also crucial to not be dragged down or saddened by them afterwards. We need to move on in joy and happiness!
What sounds more healthy?
A. Slipping up, promptly doing teshuvah but still feeling guilty or moping about for a few hours or a day.
B. Slipping up, promptly doing teshuvah, putting the past behind, and focusing on a positive happy day.
The answer is obvious but not always easy.
If you need help with the guilt then ask G-d for help — He is ready and very much wants to help! (Remember, the cow wants to nurse more than the calf wants to suckle.)
Yitzhak Sasson 