The primary source of guilt is the belief in having sinned against God.
But after this, when guilt has been established, it is denied and made unconscious, then projected, or see as disassociated from your identity.
The problem is, this then justifies anger and reactions. When someone comes along and does something and you seize the opportunity to project blame, you'll go into a reactionary attack mode.
Seeing someone as the one who is sinful, justifies all ego reactions. Then the reaction happens. Once the reaction is happening, anger is justified and attack seems to make sense.
So then you counter-attack. This counter-attack is based on the perception that the person is a "real sinner". So now you see yourself attacking a "real sinner", justifiably, and in the moment it seems like a completely rational thing to do.
But if you attack your brother, or blame them, or aggress against them, it's going to do something to you. Seeing them as a real sinner, and attacking them, means you are now attacking something "real" all over again.
This means that now your counter-attack is in fact another whole layer of sin.
And that sense of sinning against something real, even if its against someone who seems to call for attack, WILL produce yet more guilt. You might feel like you got something off your chest or put someone in their place or told them where to fuck off or whatever, but afterwards, you will feel guilty.
You can't help but be guilty if what someone did seemed like "real truth" and your response to it was attack. Attacking reality produces sin then guilt.
It can go even further in a vicious cycle, whereby now that you are guilty for having attacked, instead of facing the guilt, you will seek to scapegoat and attack yet again, maybe lashing out at someone who wasn't even involved in the original conflict, adding yet another layer of guilt on top of guilt on top of guilt.
I noticed this yesterday because I became angry at someone and felt justified in venting at them, and later couldn't shake the feeling of guilt. When I applied forgiveness, I found out that I believed I'd hurt the person, and that as a result, I believed I must be guilty. And the fact is, that the argument was nothing to do with the person really at all, it was me projecting unhealed stuff about an entirely separate person. And the issue wasn't even to do with that separate person. It was about myself, of course.
Layers upon layers.