Well.. I got frustrated with my players and put the FIVE of them against an uber boss (16 attack/16 def), four bosses (15 attack/14 defense), and unlimited waves of mooks, and I had to cheat most of my rolls to even put a hurt on the heroes so the encounter wasn't an entire cakewalk for the party.
My players had irritatingly good luck.
Now, if your mooks had a 14 av, that is exactly why everyone died. Mooks should only have about 8 or 9. 14 av mooks is almost a guaranteed party wipe, (unless you're me).
P.S. I made an encounter that was so over the top ridiculous for this group, everyone was either down or heavily impaired, and I even had someone at over 100 wound points, and they still won. (The encounter was designed for them to lose and be captured to progress the story.)
Feng Shui is unforgiving to players/storytellers with bad luck. Which is why I recommend the GM cheats for the sake of the story. Because having an important boss die after from three very lucky attacks in a row, or having a player, who's been unlucky the entire campaign, finally getting a chance to be the the big damn hero who can take down the big bad guy and save all their friends, failing because the boss made his 8th upcheck and dropper her the next attack is BAD storytelling, and basically the least fun thing you can do.
In short, screw the rules in any tabletop. Nudge rolls, ad schticks to enemies mid fight, homebrew enemy schticks, throw unlucky rollers a bone once in a while.
As a played, I NEVER roll well in any game. In tabletops, I'm the equivalent of the weird, unpopular girl who's only at the party because her best friend is really attractive. You know the type. The one that gets ignored the whole time, until she's peer pressured into doing something she's said "no, I don't want to," a half dozen times.
I want to play and belong to the group, but I'm a failure at rolling and never contribute to the party in combat, but I roleplay and solve problems, but then die because an enemy decided to attack me and the storyteller was rolling like thindar and I was rolling nothing but ones.
Honestly.. Being a player murders my self-esteem, amd more frequently than i care to admit, sends me home in tears, which is why every character I make has a horrible and tragic back story, because at least their inevitable death that's caused by my poor rolls is putting an end to their suffering.
In short, don't make your bad luck players feel like I do every time I've ever played a tabletop, and don't let your lucky, min maxing players have it too easy. Games are supposed to be about fun and making a memorable story, not making someone feel like they can't do anything right and the group would be better off without them, because without them being there, there'd be one less featured for in the encounter.
I'm not saying give everyone a trophy for showing up, but I am saying as a storyteller, you're not just a god in your fantasy world, you're in a unique position to give players happiness. Be it overcoming a nearly impossible challenge, or making a sad and depressed loser feel like she's an asset to her friends. Either way, don't make it obvious you cheat. It pisses off the good players, and crushes the bad players.