From the blog:
The problem with puzzles is 1. they either get solved trivially or 2. they stop your game dead.
Ugh, that's a sign of poor puzzle design or placement.
Either a puzzle is for an "extra", like more loot, or it is integral to moving forward. If it must be solved to move forward, there needs to be a way to "fail forward" - to assess a meaningful penalty but allows forward movements in the place of just blocking any progress.
It's like if the entire adventure is contingent on finding the hidden trapdoor under the rug and no one does.
This is irrespective to (and often in addition) to what the blogger talks about in terms of rule of three for clues (always good advice) and the rest.
There needs to be some mechanism that will penalize the characters appropriately but allow the plot to move forward even if the puzzle is never solved.
As for the case where the puzzle is not vital, that's not the case. In cases like that there should be some mechanism to encourage players not to stop play - say wandering monsters, guard patrols, outside time limits, etc. So that players can give it a shot, but not stay there and voluntarily not move forward just because they want what the puzzle guards - without a degree of risk.
I mentioned player there - and that's because puzzles are usually something that tests the players ingenuity. One point I'd like to add to the original post in terms of making them solvable is that it's the character in world. In order to bring in the character, the puzzle designer should also have clues ready based on what the characters can do. Certain ability or skills might reveal clues, spells as well. Don't worry that these make make it easy - the puzzle may be easy to genius character yet the players are just missing the obvious connection.