Grinding, the bad idea a lot of game developers have to make game-play appear longer. While I do not with to say that all grinding is bad, it is definitely overused as a tool to 'stretch' time in a game. There are 2 variants of this: The Rare Artifact and The Menial Task. While the first one is 'mostly okay' by my standards, the latter is terrible and just makes for 'wasted game time'. Especially RPG(Role Playing Games)'s are guilty of doing this a lot.
Let's analyze them for a moment.
This is when a rare item is only obtained at a very low chance. Sometimes you may have to kill hundreds of critters to find that one gem or whatever. But that's fine. When you have done so, a mountain of skulls lies at your feet while you wield your Blade of Epic Awesomeness (+1). This works.
Why? Because you feel like you have done something, put effort into achieving a goal that no one else could (easily) do. It didn't just take time, it took careful exploration, strategy, mass murder or whatever else.
Personally, I do feel that this method only works if there are viable alternatives via skill or if there is a good reason for the item being carried by pink fluffy bunnies. Also, making "The best" item only available through grinding means that anyone spending "unskillful" time can achieve it, making it relatively meaningless. ie. Slaying a mighty dragon after 50 retries is a lot more emotionally rewarding than slaying 500 bunnies.
Unless they're dangerous bunnies of course.
This is when a simple task can be repeated ad nauseam to get 'something'. Usually, this is gold or whatever. When gold provides an important part of the world, this could make sense, but most of the time it serves only as a completely meaningless inhibitor.
Because skill(statistics/level/actual player skill) should be the only thing limiting a player to use an item, not price or anything else. Using gold (or any other arbitrary system) means that grinders get rewarded while people with skill get punished. Using gold as an inhibitor only works if it is a limited commodity, as then it becomes a strategic choice. Do I spend it on X or Y?
RPG - Dragon Age: Origins - Gold is easy to obtain through grinding, but not so much through questing. Similarly, DLC(DownLoadable Content) added items that can be sold for a significant chunk of gold giving those that own the DLC an unfair advantage. - A solution: Give crafting random awards or do away with most of the steep prices. There's nothing wrong with using gold only as a "background object".
RPG - Mass Effect 2 - Here we have a perfect example. For your upgrades you need Element X. How do you get element X? Well, you buy probes, then send those probes to a random planet. To stock up on X, all you lose is some time to go from planet to planet, probing, getting X, rinse and repeat. Oh, and every step is fairly slow too. No skill involved, just really, REALLY boring clicking and waiting. - A solution: Do away with the element X requirements as all upgrades need to be acquired anyway (either by levelling or exploration)
Sandbox/gathering games are exempt of this rule. There, the point is exploration and creating items to furthen your goal. Minecraft and Terraria are perfect examples of this. But here you two find 2 'types' of players. The kind that doesn't care for the grind and just uses a hack to get materials for building and the kind that likes the feeling of achievement by chopping away an entire mountain. Neither group is 'wrong', it's just different ways to play.
But they are sandbox games, their whole point is that you decide how you play.
_ps. I would have added examples from Final Fantasy, but I don't know them well enough off the top of my head. I also want to side-note that both Dragon Age as well as Mass Effect are fantastic series._