Karmic consequences usually alter the character of the actor. When people do bad kamma, it alters their character for the worse.
They may think: “When the time comes, I’ll do some good deeds.” The problem is, they’re slipping down all the time, so when the time comes, they forget about doing good deeds. They simply ignore them—that’s the way it tends to go.
When one slips down, climbing back is hard work. It’s easy to go down but difficult to get up.
That’s why it is best to avoid even small instances of bad kamma; they easily turn into habits that become a part of one’s character. When that happens, one’s character becomes altered, sometimes irreparably.
p161-162 Uncommon Wisdom by Ajahn Pannavaddho