DM and Old School Roleplaying Challenges Theory

Reading about role playing, I found the concept of Old School Roleplaying (OSR) -style challenges.  They were ones that fulfilled:

• No obvious solution.  (Straight combat is always obvious.)
• Many possible solutions.
• Solvable via common sense (as opposed to system mastery).
• No special tools required (no unique spells, no plot McGuffins at the bottom of a dungeon).
• Not solvable by a specific class or ability.  

There is a big list at a Goblin Punch page.

The categories from that page seem to be:

• Environment works against your goal.   
• What you need depends on something that needs to be triggered.  
• A moral quandry - applying a moral problem to the game world so it now has an effective outcome.  
• A thought experiment applied to the environment.  
• Stopping a group of people from doing something, with a twist.
• "Impossible" battle, which may have loopholes.