'I'm willing to give up x% of my company. How much cash will you give me for it?' In theory, that should be the same as saying 'my company is worth y% of what

'I'm willing to give up x% of my company. How much cash will you give me for it?' In theory, that should be the same as saying 'my company is worth y% of what company Z is worth, so this is how much cash you need to pay in order to get x% of it', but in practice, you can't always make that conclusion based on how people behave.