Karma and one's own belief about the event

The Parable of the Salt Crystal from the Lonaphala Sutta:

"Suppose that a man were to drop a salt crystal into a small amount of water in a cup. What do you think? Would the water in the cup become salty because of the salt crystal, and unfit to drink?"

"Yes, lord. Why is that? There being only a small amount of water in the cup, it would become salty because of the salt crystal, and unfit to drink."

"Now suppose that a man were to drop a salt crystal into the River Ganges. What do you think? Would the water in the River Ganges become salty because of the salt crystal, and unfit to drink?"

"No, lord. Why is that? There being a great mass of water in the River Ganges, it would not become salty because of the salt crystal or unfit to drink."

"In the same way, there is the case where a trifling evil deed done by one individual [the first] takes him to hell; and there is the case where the very same sort of trifling deed done by the other individual is experienced in the here & now, and for the most part barely appears for a moment.

'Now, a trifling evil act done by what sort of individual takes him to hell? There is the case where a certain individual is undeveloped in [contemplating] the body, undeveloped in virtue, undeveloped in mind [i.e., painful feelings can invade the mind and stay there], undeveloped in discernment: restricted, small-hearted, dwelling with suffering. A trifling evil act done by this sort of individual takes him to hell.

'Now, a trifling evil act done by what sort of individual is experienced in the here & now, and for the most part barely appears for a moment? There is the case where a certain individual is developed in [contemplating] the body, developed in virtue, developed in mind [i.e., painful feelings cannot invade the mind and stay there], developed in discernment: unrestricted, large-hearted, dwelling with the immeasurable. A trifling evil act done by this sort of individual is experienced in the here & now, and for the most part barely appears for a moment.

And more explanation in MN36:

"And how is one developed in body and developed in mind? There is the case where a pleasant feeling arises in a well-educated disciple of the noble ones. On being touched by the pleasant feeling, he doesn't become impassioned with pleasure, and is not reduced to being impassioned with pleasure. His pleasant feeling ceases. With the cessation of the pleasant feeling there arises a painful feeling. On being touched with the painful feeling, he doesn't sorrow, grieve, or lament, beat his breast or becomes distraught. When that pleasant feeling had arisen in him, it didn't invade his mind and remain because of his development of the body. When that painful feeling had arisen in him, it didn't invade his mind and remain because of his development of the mind. This is how one is developed in body and developed in mind."

Always chethana(thought) is the karma. The thought when you are yelling already brought you a karma. If you are going to think about it again in a good way or bad you just sum up new karma. Every thought belongs to one of six fundamental thoughts loba, dhwesha, moha, aloba, adhwesha ,amoha.

Revisiting your past bad deeds with wisdom and determining not to repeat is good Karma. Regretting your past actions is bad Karma.

In my tradition we recognize three ways to do repentance.

On the basic level, we should feel ashamed and guilty, tell someone about our misdeed, then decide not to repeat same mistake. Then stop beating ourselves about it, since that only makes things worse after certain point.

On the medium level, we should understand that our mistake was because of a particular delusion or reification that manifested as some sort of attachment, which then produced the behavior. We should make an effort to really see our preconception or overgeneralization or attachment that gave rise to the misdeed, and make an effort to let go of it.

On the highest level, repentance consists in simply recovering the stable and pure state of mind and staying in that.