Playtest, playtest, playtest. Even folks who only play games, and never make the transition to designing, know that playtesting is an integral - maybe even the integral - part of the process. A common refrain when a game disappoints us is, "Did they even bother to playtest this?"
There are various reasons why we playtest. First, to make sure the game works as intended; second, to make sure the game is fun; third, to catch and eliminate ambiguities; fourth, to make sure that there's some decent amount of replayability; fifth, to ensure the game's balance isn't broken. And there is a general expectation that designers and publishers will provide games that work, are fun, are unambiguous, are replayable, and are not broken. That is, I think, a completely reasonable expectation.
I don't think, however, that that expectation extends to catching every single possibility. For example, I had someone who owned one of the original Shields & Swords games tell me that the game was hopelessly broken. I was a little shocked to hear that, and asked the player for more information. They explained that since there was no limit on the number of game turns, and that since players during a movement phase may move "any, all, or none" of their units, that both players could simply refuse to move, and the game would go on forever. "These are the kinds of things you need to catch!" he said.
"Did you play it that way?"
"No, but someone could do that. So the game is broken."
(It was as a gentle tweaking of that gamer that I included the "Don't be boring and dumb" rule in High Speed Hover Tank.)
So, let me just say, if you're reading this and you're nodding your head in agreement with that guy, then, I'm sorry, but maybe we can't be friends anymore? Because a definition of "broken" that involves both players acting like smug brain-dead jerks is not a definition that I can ever get behind.
"War of the Ring", photo by Adrian Wiechec
And I find that as I get older, and I work on more games, and I try to make those games more interesting, I'm kinda having trouble getting behind definitions of broken that involve even just one player acting like a smug brain-dead jerk. For example, I remember reading years ago about SPI's War of the Ring and its Mount Doom "strategy" that consisted of Sauron stacking everything he had in that one hex and twiddling his thumbs for the rest of the game, making it impossible for the free peoples of Middle-Earth to destroy the one ring. And at that time, I thought, jeez, that's broken, how did no one ever think of that? Did they even test the game?
But now? If I was sitting down to play that game with someone, and they pulled that stunt? I would probably say, "Yeah, that's cute, can we really play the game now?" And if my opponent went all "I am playing the game, this is totally allowed in the rules, this is a perfectly valid strategy," at that point, I'd find someone else to play with.
Would the game be better if someone had tried this during playtesting? Sure, probably. Do I feel that the developers were derelict in their duty because they didn't anticipate someone acting like an obnoxious prat? No, not really. Not anymore, anyway.
My general assumption is that when two folks get together to play a game, that they're both looking to have fun, and that their definition of fun isn't to be obnoxious. My job is to facilitate that fun, and in doing that, I'm going to assume a certain degree of good faith.