In real life, if you fight and "lose" you die.
Belegarth has the distinct advantage of being able to LEARN from your mistakes.
If a fighter seriously outmatches you, your gonna lose. So? Set lower goals. See how much of his armor you can take first, see if you can get a limb or something.
Often, when I know someone is way over my league, I just see how long I can work my shield blocking his shots. If an opening becomes wide open, sure I"ll take it, but until then I just bide my time and work on my shield work.