I love speculative fiction: always have, probably always will. There's something fantastic about the fantastical and whether this is a whole new world as in high fantasy or hard science fiction, or a "relatively real" world such as in urban fantasy, steampunk, cyberpunk, magical realism, and alternate-history/-futures, it's vitally important that the world as perceived through the eyes/nose/hands/brain of the main character be solid as adamantium. It has to make sense--externally and internally--and while I still believe that the author is not obliged to answer every question in the text, as a reader, I have to somehow believe that the author *could* answer any question I or anyone else could come up with quickly and easily. If they believe in their world, I believe it, too. It has to stand up to being poked, prodded, turned every which way, having its tires kicked a few times and cross-examined by your date's parents. (Remember, fanfic is in the "what ifs" that crop up in our wildest imaginations because we want to believe!)
If the author says that this tavern can't be found unless you were somehow meant to find it, then okay. I believe you. The author does not have to prove it with physics or magic or outer-space conspiracy theories, the statement is enough. But what this means is that at no time can someone blunder into the place and be told "you're lost", "you're in the wrong place" or "you don't belong here." According to the internal rules that the author has created that uphold their world, this previous statement has to remain constant. The moment it wavers, it pops my balloon* and the air leaks out...as well as my suspension of disbelief. It is no longer suspended. I'm sunk.
And then I'm disappointed. Or worse, angry. Or worst: I put down the book and walk away. Bad, bad, bad! Don't let that happen!
In essence: is your world strong enough to withstand questioning?
Here's a handy test: take the entire story and turn it at a sharp, widdershins angle and look at it from another character's point of view: does the story still hold up? As an example, let's look at the story of Harry Potter from the point of view of Severus Snape...
Young Severus was a scrawny, not very popular young wizard who had a crush on the only girl who was a) nice to him and b) from his corner of the world, Lily. Imagine how he feels when she starts dating one of his worst tormentors and, worse yet, goes on to marry him and have his baby! (A child of ill-fated prophecy, no less.) Snape is a bitter boy, abandoned at Hogwarts, turned inward and quietly raging about the unfairness of it all, knowing secretly that he's better than some of his teachers. (Hence the Half-Blood Prince scribblings.) How he savors his own power and longs for a way to express it, to best them all! It's no wonder the lure of the dark calls to him and that Death Eaters, those who instill fear in their enemies and are brimming with power, entices Snape as well as their leader, Voldemort, the "mudblood" who rises above everyone who cowers in fear.
However, Severus makes his break and sides with Dumbledore; a great wizard and Headmaster who recognizes Snape's talents and believes in his contrition, taking him into the most strictest of confidences and trusting him "with his life" (which, given his terminal condition tempered by potions, is quite literally true--mentioned in the very first book and brought to light in nearly the last). Now Severus lives up to his own self-image, being a very important, integral part of the powerful world of Hogwarts not only as a teacher, but as a potions master to and for Dumbledore, a key player as a double-agent in the war against Voldemort, and an insider to the intricate games being played between wizards and politics and men. His is a secret power that gives him a warranted arrogance and one-upmanship. His past gives him a cloak not of invisibility, but fear, and that suits him better.
Then into all of this is thrust the boy of the prophecy, the one who bears his father's surname and his mother's eyes. Oh how Harry Potter must be a symbol of everything unfair and "What If?" and "Why?" to Severus Snape! It is the wrestling with the ghosts of the father that make Snape so reactive to Harry, getting a bit back from the time when he could not against James, and yet there remains the furious need to protect and honor the love he felt for Lily and make sure the prophecy can be fulfilled, which is paramount to everything (even Dumbledore's life). And in the end, Snape is worthy of the challenge: compassion and love wins. Severus Snape does everything he can for those he has taken as his responsibility: Dumbledore, Draco Malfoy, and even Harry Potter.
He is a complete character. This saga could be his. If we take the world and see it from his point of view of a life lived and served, the story still makes sense. JKR's is a *solid* world and can take the slings and arrows of outrageous questioning** and still come out intact. That is the sign of a well-built world and a fictional character's life well-lived.
* You don't want it to pop like a balloon. You want it to be a solid balloon! (Not to say it should go over like a lead balloon; that's something else.)
** Not to mention outrageous fanfic! ;-)