‘when you have eliminated the impossible, whatever remains, however improbable, must be the truth’
– Arthur Conan Doyle, The Sign of the Four, 1890

In other words: When you’ve checked everything you think likely without success, you need to start investigating the things you dismissed as unlikely.

‘A journey of a thousand miles begins with a single step’
– Laozi

In other words: If you have to implement an ‘epic’, you need to think about it in terms of smaller units of functionality.

‘Il semble que la perfection soit atteinte non quand il n’y a plus rien à ajouter, mais quand il n’y a plus rien à retrancher.’
– Antoine de Saint Exupéry, Terre des Hommes, 1939, p. 60.
(‘…perfection is finally attained not when there is no longer anything to add, but when there is no longer anything to take away’
– Lewis Galantière)

In other words: Don’t check in dead-ends that didn’t actually solve the problem.

‘The point is, it’s not productive to ask questions like “Do most people like pulldown menus?” The right kind of question to ask is “Does this pulldown, with these items and this wording in this context on this page create a good experience for most people who are likely to use this site?’
– Steve King, Don’t Make Me Think! A Common Sense Approach to Web Usability, Second Edition, 2006, p. 129.

In other words: Speaks for itself!