If you're asking how to prevent a one-time event from happening again, the answer will depend on what the event was. If it was something like a car accident, then you can't do much to prevent it other than drive more carefully in the future. However, if the event was something that you had control over, such as getting into a fight with someone, then there are things that you can do to prevent it from happening again.
Some tips for preventing fights include: communicating calmly and respectfully with the person you're arguing with; trying to see their perspective and empathizing with them; walking away from the situation if things start to get too heated; and being willing to compromise. If you can learn to handle disagreements without resorting to violence, then you'll be less likely to get into fights in the future.