And, occasionally, they don't follow the "rules" laid down by gardening experts. For instance, I had a a Greater Meadowrue (Thalictrum aqulegifolium) rambunctiously reseeding in a hot (for Seattle) dry, sunny, sandy site when the usual instructions call for rich, moist soil in sun or part shade.
And then there are the bog plants that somehow manage to thrive in quite dry areas, perhaps because many wet sites dry out in summer.
But ignoring instructions isn't a good idea, either. In general, they're based on solid know-how, though I have a suspicion that one person's experience gets passed on from writer to writer without much testing. If you buy one or three plants, you don't want to stress them unnecessarily.
But if you have seedlings, maybe from a packet you planted, feel free to try a few in less traditional sites, maybe a little more shade, or a little less water once they have a good root system. Short dry spells, in particular, can be quite good for roots, forcing them to grow more quickly.
And then there are the plants that you treat exactly according to instructions that just, for some reason, refuse to grow. Every garden's different. And sometimes there's a factor no one mentions.
For instance, I never could grow nasturtiums until I planted them in light, freshly dug soil. They seem to need the extra air. And I couldn't grow Angelica for quite a while, then suddenly they started doing fine.
Whatever happens, don't get discouraged. Just start over. And over. And over....
Cardoon, an enthusiastic accent plant that's also edible. And it doesn't seem to care much where it's planted, no matter what the instructions say.