I too dont see the point in brooding over a loss or a wrong decision. These things will not end but repeat but you get only one life which should never be wasted on regret. However I do agree that often in the young age people do stuff that they end up harming themselves or someone and that they regret such in future. I would say that living a disciplined life from one point reduces such incidents.

In investing, always learn from mistakes and try to not make the same mistake in the future.