The regret / guilt or repentance associated with an action that caused pain to someone else is much less than that which caused you pain.
Hence when people say “I regret I did that to him”, I’m forced to think how much they think about it with respect to “I regret I did that, coz it left me this way”.
I wish we could understand the pain of others in the same light as ours. Sadly it isn’t possible.
No matter what one does, one cannot step into someone else’s shoes and claim to ‘understand’ the pain.