I'm a fairly patient gardener compared to most. I'll give a poorly-performing plant a decent chance before I relocate it, or even banish it. Usually this means an entire growing season, but sometimes it means a few years.
Take for instance this 'Fine Line' buckthorn, Rhamnus frangula. I picked it up at least 5 years ago at a bargain price, and envisioned it forming a column of green, feathery foliage.