to be successful

the obvious things is most people want to successful.
the next obvious thing is to be successful you need to have a success.
the next to next obvious thing is that to have a success you need to have worked on a successful endeavour.

the darnedest thing, is how would you know if that endeavour would turn into a success!

another way of saying this in advertising parlance:

the only advertising that works is the one consumers have noticed and remembered.

the darnedest things again would be you don't know which one would be noticed and remembered.