Important logical principle to take away from [WayBack] The dialog manager, part 2: Creating the frame window – The Old New Thing:
If you’re not sure whether something is true, ask yourself, “What would the world be like if it were true?” If you find a logical consequence that is obviously wrong, then you have just proven [by contradiction] that the thing you’re considering is indeed not true.
Thought experiments like these can really help you get a feel for parts of a problem before you completely resolve the full problem.
Related: Thought experiment – Wikipedia
–jeroen