Why can't i grow cosmos?

I've been trying to cultivate cosmos, but it seems like no matter what I do, the plants just won't thrive. Could it be the soil? The watering schedule? Or maybe the amount of sunlight they're getting? I'm at a loss as to why my cosmos refuse to grow. Could you possibly offer some insight into what might be causing this issue? I've been following all the recommended care guidelines, yet the results are still disappointing. Any advice you could provide would be greatly appreciated.