1 Eleven: So what’s at the end of this crawlway passage?
2 Lucas: A dead end. Or apparently so. There’s a secret door that each person has a 1 in 6 chance of finding, regardless of race: elf, human, or dwarf.
3 Dustin: That means if all four of us search, we only have a 51.8% chance of finding it.
4 Eleven: Why would they have a thing with such a high chance of completely halting any progress in an adventure?
4 Dustin: Because it’s fun!

Yeah, that's a thing in the Tomb of Horrors. There are secret doors that are specified as more difficult to find than in the usual rules, with a fairly low chance. And if nobody in the party finds them, there's no way to progress further in the adventure.

This is one major drawback of linear adventures, of which linear dungeon designs are one example. If the heroes miss one clue or secret, they can end up being completely unable to progress and finish the adventure. In the glory days of the 1970s and 1980s, this was considered amusing and all just part of the game.

More modern dungeon adventure design makes use of concepts outlined in this now classic series of blog posts by The Alexandrian: Jaquaying the Dungeon and its follow-up parts. If you ever find yourself writing your own dungeon adventures, you really should read this. It will without a doubt make your dungeons better.

To summarise briefly: You want multiple paths and connections to reach any part of your dungeon layout. Give the players options. If one route is blocked by a trap or an encounter they don't want to face, they have other ways to get around them. And if they fail to spot a secret door, they don't miss half the dungeon that you carefully designed. They get there some other way.

Seems obvious. But go read the articles, and realise you can almost certainly improve your dungeon layouts.