I agree with the reply that Savi posted to your question in another thread. You're really not stuck until you have 'purchased' L3 in every technology and have played for at least a day after that - it can take some time for those little people to get everything done!

Some puzzles require specific levels of technology and villagers with specific skills.

The 12th puzzle is designed to be very, very difficult, so it will take some real work to solve it.