Guys, how do you stay interested in megaprojects?
Dedication and real desire to be able to be proud of what you complete. If you want to be proud that you built the Colosseum in Rome in Minecraft, you have to actually DO it. If you don't want to reap the benefit of completing megaprojects then you won't feel the need to do them to begin with.
Or you could have an actual need for them, i.e. a man-made river in order to link two other rivers in your survival game.