Every time this happens, cosmic forces are disturbed and mark ever so imperceptibly the agent of the disturbance. So the simpler way to check this out is to roll percentile dice. For example, a PC defeats a 20 HD dragon and carries the final blow, roll percentile dice.
Fate is fate, whether good or bad.
This isn't good. Because from this point on, accumulated karma points act as penalty modifiers to future karmic rolls. So for example, a PC has accumulated 5 points. If he defeated that 20 HD dragon again, the score to roll would then be 25 or less. Eventually, the agent's life begins to suffer the effects of cosmic reprisals.