This post exists mostly so that I can link to it in the future as an anecdote on why random drops can be a problem.
Towards the end of The Lord of the Rings Online™: Shadows of Angmar™, I decided to get the Annuminas armor set. There are six pieces. You barter for three with items that can drop from every enemy in the sub-zone; get a few hundred and you are set. The other three require barter drops from the bosses of the three Annuminas dungeons. Each boss always drops one barter item, which trades for the relevant armor piece for each class. Turbine used this boss barter drop system for all the dungeons and armor sets in Shadows of Angmar™ and Mines of Moria™, before moving to a more pure token system in Siege of Mirkwood™.
The downside here is that you can lose. You know the guy who beat Boss X 46 times before he got his magic boots? My number was 16. I was running at least one Annuminas dungeon most nights that I played, frequently unsuccessfully because every group included at least two people who had never been in that dungeon before. Some nights I waited a long while without ever getting a full group, and some groups broke up after half the team wiped on the way to the dungeon. (Annuminas was a rough neighborhood in those days.) Out of 16 successful runs, I won the roll once.
That is not even a terribly unlikely outcome. You will lose 15 of 16 1/6 bets 6.5% of the time, and you will lose all of them 5.4% of the time. 1 in 11 people who will have my luck or worse on that roll. [Update: I think my original math here was wrong.]
Me? I quit. I left LotRO for at least six months, checking out Mines of Moria™ halfway through its lifespan only because I already had a lifetime account. There was just one thing in the game that I really wanted to Achieve, I had spent at least 40 hours on it (between waiting and in-dungeon time), and I had one piece of armor to show for it. The dungeons stopped being fun the tenth or twentieth time I had to explain “keep the silence-aura ghosts away from the healer.”
“Almost 1 in 4” is a lot of players to potentially lose on a 1/6 roll. My odds might have been better if I had a guild that ran those dungeons consistently, but pull me from the PUG pool and you have even more groups failing. Remember, that was 1/16 successful attempts; these are not fast, faceroll-easy heroics. You get a lot more tolerance for unfortunate luck on the prize roll when the win is all but guaranteed.