Between two stools

Meaning

Fail, due to being unable to choose between two alternatives.

Origin

This is an old phrase. It is first cited in John Gower's Confessio Amantis, 1390:

"Bot it is seid - Betwen tuo Stoles lyth the fal..."

The first recorded use in modern English is in Matthew Prior's comic poem Alma; or, The Progress of the Mind, 1717:

Now which were wise, and which were fools?
Poor Alma sits between two stools;
The more she reads the more perplex'd,
The comment ruining the text:
Now fears, now hopes her doubtful fate.