On the other hand I think there are definitely situations and play styles where the player resorting to a wiki is a failure of game design. I mostly don't use wikis, but if I get into a situation where I don't feel like I'm making progress or have any idea what to do ("how do I even damage this boss at all?"; "I feel like I spent the last half hour wandering over the map and I have no clue where I need to go next"; that kind of thing), then I'm likely to look up the answer. And once I've found a walkthrough or wiki I'm probably going to keep using it even when the next part is less annoying. I think in that kind of case both the player and the designer are likely to feel it would have been a better game if that resort to the wiki was avoidable.

There are also situations where I will happily look up a walkthrough because I've had enough "puzzle solving" fun and just want the "see the last bits of content" fun before I put the game down. I did the tail end of Tunic and Fez that way. This kind of thing I don't think is a game design failure -- it's just different players having different preferences for how much and how complicated they like riddle solving and secret finding gameplay.