そうは問屋が卸さない
Meanings
1
things don't always go as planned; it's not that easy; the wholesaler won't sell it like that
Idiomatic expression meaning that things rarely work out as smoothly as one hopes, often used to temper expectations. The literal image is of a wholesaler refusing to sell goods at the buyer's desired price or terms.
If you think it'll go that smoothly, you're mistaken. Things don't always work out that easily.
He thought he'd get promoted quickly, but it wasn't that easy.