Plant a plant, begin an experiment. Does the plant establish? Does it look good as it matures? Do you keep up with the maintenance it needs, and are you and the plant both screwed if you don't? Ultimately, does the plant do what you thought it would? Either way, do you like it or do you say "What was I thinking?" Is the experiment ever over, or does it morph into new ones?
When I planted the orange-twigged lindens that I've since trained into a long espalier, I flanked the main passage through it with upright Japanese hollies. I also planted a weeping gold-barked ash, thinking that someday its lax branches would cascade down like a Victorian curtain at the side of the opening.
Fifteen years into the experiment, there's still no cascade, but there is plenty of splay. Fall foliage shows how this unexpected outcome isn't just fine, it's fabulous.