Boris the town guard tries to disarm Edgar the Rogue. He’s at +8 to hit and using a broadsword. He is (+8-8=) +0 against Edgar’s +12 shortsword. He rolls well – an 18, and Edgar rolls d20+12 for just 16. Edgar’s shortsword goes flying and he raises his hands in the air. It’s a fair cop.
Boris’ investigations into a crime ring leads him down a dark alley where Lady Seera is hiding. He draws his trusty broadsword and hears the rattle of a chain in her hands as she lunges. She’s +10 with the chain, and tried to trip him so she can run past next round. She is (+10-4=) +6 against Boris’ +8 and rolls a total of 21. Rolls lucks out with a natural 20 for a total of 28, easily avoiding the trip attempt. Seera bares her teeth in a snarl, revealing long, vicious incisors. Boris thinks maybe that was one roll it would have been better to fail…
Slightly more complex example: Boris has been sold into slavery by the crime ring. He finds a chance to escape one night and ends up fleeing through open country for his life. A lizardman chasing him throws a mancatcher spear. It’s a longhafted weapon with a hinged circle of iron at the tip designed to snap shut around a captive’s neck. The lizardman is at +9, -4 for range and -4 to hit the neck. That’s d20 +1 for a total of 11. Boris is +8, -4 because he’s unarmed and at a big disadvantage. He rolls a total of 7. The impact of the spear sends him flying into the mud, the iron jaws snapped shut about his neck. Things don’t look good for Boris.