"No pain, no gain", said actress Jane Fonda in her aerobics workout VHS tapes of the 1980s. Or so I heard. From a friend.
It's a simple but smart little adage: it means nothing's ever easy, no one gets anything without a degree of hard work, and the more difficult something is, the more satisfying you'll feel when the whole ordeal is over.
It works in games, too.
If a game's too easy, you'll sleepwalk through it and feel no sense of reward or satisfaction at the end. If it contains a particularly tricky section that you have to replay 20 times, you'll be doped up to the eyeballs in dopamine by the time you clock it.
These ten iPhone games, from bullet-hell shooter DoDonPachi Resurrection to chin-stroking puzzler The Heist, will all push your brain and fingers to the point of pain. But show these apps who's boss, and you'll be swimming in that sweet, sweet reward juice.
DoDonPachi Resurrection (buy)
In this manic bullet-hell shmup from Cave, you'll spend more time dodging bullets than actually firing them.
As you dart and dive through the game's rock-hard stages, menacing enemies will spill out screen-filling ordinance in giant carpets, waves, and tendrils. It's your job to navigate your tiny spaceship into the narrow gaps, and stave off death for another few seconds.
In fact, DoDonPachi's iPhone edition is all about dicing with death - the closer you float next to incoming bullets, the higher your score multiplier will climb. You'll need balls of steel and a seriously steady hand to reign on this game's exclusive leaderboards.
League of Evil
As a pixel-art platformer in the same vein as ultra-hard jumper Super Meat Boy, League of Evil has you jumping over spiky death mallets, between temperamental lasers, past nuisance bodyguards, and down perilous shafts in tow of the eponymous ring.
Luckily for you, the game sports ultra-responsive controls that let you move your pint-size hero with grace and confidence, including gravity-defying double jumps and Mario-style wall leaps.
Unluckily for you, they matter little when the game is this tricky. Levels quickly get harder, faster, and bigger as the game goes on. And if you have the mettle to beat the lot, you'll be rewarded with the suitably named "The Impossible Missions."
I can't do level 1.
Tilt to Live
Calling Tilt to Live a shooter would be silly: unless you pick up a power-up, you can't shoot enemies at all. Instead, you must zip and dart about the claustrophobic play area to avoid the game's merciless red dots and hope a suitable item appears.
As the name might suggest, TTL is about tilting. The only way to play is by shaking your iPhone or iPad about like someone's drawn a rude picture on an Etch A Sketch. It certainly gives the game a tactile and hands-on feel, but it can make it as hard as hell to guide your hero through a tiny gap or around a swarm of dots.
Things don't get any easier in Code Red mode, which ramps up the difficulty from the word go. As soon as the level launches, you'll be inundated with murderous red dots, and it's all too easy to unlock the achievement "Our Pity" (for dying within five seconds of starting). Whoops.
Just last week, New Zealand biker dude Jed Mildon made extreme sports history by pulling off the world's first Triple Backflip.
Jed should have just stayed indoors and played Touchgrind BMX on iPhone: you'll be pulling the ridiculous move off during every other run.
BMX subverts the rules of reality and physics to let you do things like backflip to upside-down bike spin to tailwhip without landing in traction. But actually pulling these ludicrous, point-scoring tricks off - without ever bailing to keep your combo running - is as hard as nails.
You'll need to be doing several different swipes, taps, and gestures on your touchscreen, while making sure your bike will be suitably upright by the time it hits the ramp. You'll also need to avoid any and all obstacles, and contend with a nauseating first-person camera.
Not for the fainthearted, that's for sure.
This fast-paced skiing sim is one tricky little indie game. It's learning curve is steeper than the Alps, and you'll definitely tumble off into the abyss about six million times before you properly grasp the controls.
In Solipskier, your job is to draw in the snowy mountain range as the tiny skier automatically slides along towards his inevitable doom. You can create peaks, troughs, dips, and jumps for him to skate across.
You'll need to guide him through rings and over leaps to earn the most points, but until you master the game's many nuances, you'll probably end up turning your skier into a jumbled mess of bone and flesh at the second leap. Or maybe I'm just rubbish: who knows.
The Impossible Game
Has a game ever had a more suitable name? This rock-hard platformer is almost unbeatable without a million attempts, the reaction speeds of a cheetah, and the patience of a saint.
You play as an orange square, and you simply tap the screen to leap over triangles and land safely on black boxes. Sounds simple enough, but as the game ramps up speed and makes the jumps ridiculously close, you'll die over and over and over again.
You can, thankfully, drop a checkpoint down so you don't have to start the stage again each time you mess up.
Unfortunately, you give up more points if you use them, so the most hardcore gamers will have to go without, and finish the entire run in a single attempt. Good luck!
Canabalt isn't about winning. Much like real life, it's inevitable that you'll one day die - and lose the game.
Canabalt is just about seeing how long you can stave off the pearly white gates as you run for your life, over rooftops, and through plate glass windows, before you finally topple off a building and slam into a billboard.
The game couldn't be simpler. Your monochrome man simply runs: automatically and forever. Tapping the screen makes him leap, which is handy seeing as he's running along the rooftops of a war-torn metropolis.
It's easy enough at the very beginning, but the game starts ramping up the speed, and difficulty, within seconds.
You hit the jump button too late? Game over. A building is slightly higher than expected? Game over. A pigeon makes a noise outside? Game over. Just like real life.
Most of the games on this list are about having fast reactions and super human dexterity. The Heist is more of a cerebral affair: tricky-as-hell puzzles that will make your brain blister, not your fingers.
Through 60 puzzles - based on pushing blocks, sliding tiles and placing runes - you'll need a good memory, a penchant for spacial reasoning puzzles, a Sudoku champ's skills, and a bundle of patience.
Still, you'll get something good if you beat them, and we're not talking achievements or a warm fuzzy feeling in your belly. You're greeted with a real prize for completion, worth about a fiver. We won't spoil it, but it just about warrants all that knuckle-biting in the tile-sliding puzzles.
Developer Semi Secret Software is no stranger to punishingly difficult titles. After Canabalt, the indie dev churned out iPhone physics game Gravity Hook.
Like a vertical Canabalt, your job is to try and climb as high as humanly possible until your inevitable demise. You'll use a robotic grappling hook to latch onto nearby buoys, and pull yourself up. Fluff up your momentum, and you'll either careen into an explosive mine or not have enough speed to reach the next grapple point.
Gravity Hook is smart, sophisticated, and well-made, but it's extremely challenging and just the sort of ultra-hard game that will have masochists playing till three in the morning, and causal bods quitting in three minutes.
Super Stickman Golf
Imagine the humble game of crazy golf, mixed with the invertebrate warfare of Worms. Super Stickman Golf is all about carefully aiming your next putt, accounting for dips and grooves in the landscape, and charging up an appropriately powered swing.
It seems easy enough as you begin. Pop a ball up high to arc over a hill and plonk it into the hole with a putt. In fact, in the first stage you'll be doing hole-in-ones and eagle shots, before ending with a score that's well below par.
But then you'll unlock levels on the Moon, stages with conveyor belts, volcanic inferno stages, and other hazardous worlds.
As soon as the levels starting turning into maze-like caves with water, fire, and another annoyances, you'll be lucky to get anywhere close to par without some serious practice.