What do people "build" when they make unrealistic plans for the future?

Very interesting, as Spock would often say when it didn't qualify for his usual remark: Fascinating. Check out Jimi Hendricks' song about castles in the air.

I've heard of castles on the sky, but never heard this idiom before... The more you know.

Every time you buy on lottery ticket. Your realistic plans set in.

Mel, castles in the air are just fantasies of doing something. sand means they are not built with solid foundations! Get something going and it fails!

Tony, will do thanks

It’s actually “castles in the sand” which can wash away.

it's the only thing I can build

Just the two of us building sandcastles…….