Some seeds fell on stony soil - and flourished!!

This spring we tried to grow sunflowerrs. We bought seeds, and planted them all in small, soil filled pots. We placed them in a warm spot, watered them, covered them up when frost threatened and generally loved them. Other trays of other seeds did really well so our method seems OK. However, only three sunflower seeds came up!
We planted the three seedlings and they all grew but slowly, so we still don't have any sunflowers in our garden.
This picture shows a pile of gravel in a carpark behind a supermarket. I suspect the gravel was swept up in the early spring, and then forgotten. But here, in this unloved pile, a seed germinated, grew and flourished. This pile of gravel did better than our garden as far as sundflowers go!  I'm sure it's a metaphor for something, but the parable of the seeds it isn't!
Maybe next spring I'll fill a few pots with gravel, swept up from a dusty pavement, and shove in a few sunflowers seeds, and leave the lot in a corner of the garden for a week or two and see if more than three seeds germinate!