Three incidents.
Case one: Level five, heading along the road between Windhelm and Whiterun. Pass a patrol of Imperials escorting a prisoner, who sneer: 'Imperial business, be on your way.' Sure whatever. I jog on ahead and reach Valtheim Towers where the bandit lady tries to extract a toll from me. When you are level five, 200 gold is a lot of money, so I decide to kill her then race off before all her bandit buddies race out. Five seconds into the fight the Imperial patrol arrives. The bandit lady falls very quickly, but that isn't good enough for the Imperial patrol and Stormcloak prisoner. They instantly go charging into the tower and go on a rampage. Within five minutes, every single bandit is dead, as well as the prisoner and two soldiers. I got to loot the entire place for doing nothing. The two surviving Imperials made sure to sneer at me: 'Imperial business, be on your way' as I looted everything of value. LA LA LA CAN'T HEAR YOU Oooh shiny!
Case two: Wanting to level up my fighting skills, so I'm off to fetch Amren's Sword from (I think) Silent Moons Camp. One around Whiterun near a giants camp that has lots of bandits outside and very few inside. I march up and shoot two arrows at the lookout, then am engulfed in fire as a dragon decides to attack, enraging a nearby two giant and two mammoths who come charging over. Not wanting to get trodden on by any of those five monsters, I quickly run a little away and watch them duke it out. By the time the dragon falls, they are pretty close to Silent Moons Camp, and their bloodlust isn't sated. To my great astonishment, they promptly march in and spend about two minutes systematically killing every bandit they can find. Then they all stroll calmly back to their camp, pausing only to send two mudcrabs into orbit. So much for my plan to level up my combat skills on THAT mission.
Case three, my personal favourite: Lydia and I have just met with Thorald's brother and his two friends at Northwatch Keep, and I spend a little time listening to their reasons they want to rescue their precious, beloved Thorald from the evil Thalmor clutches as soon as possible. The plan is apparently to fight our way in, get Thorald out, and fight our way out! Right, lets start! Don't worry Thorald, we're coming for you! I sneak forward, trying to spot the nearest Thalmor and get a few shots in before the inevitable bloodbath. Quite surprised at how far I managed to get before my cover is blown, I turn around. Lydia, Avulstein and the two friends had decided to run about fifty meters down the coast to kill some horkers who got mad at me infringing their personal space while my housecarl and I were making my way to Northwatch Keep. Sorry, Thorald, first things first...You'll just have to stay in the grips of the Thalmor torturer a bit longer...