A *working* SD starter is...

... like a decent job.

Once you have either one, don't lose it until you already have another. ?

This rule is in both cases often successfully broken, but it's still good to keep in mind anyway. If you're going to switch your working starter to a different method, switch half of it - keep the original going "the old way" until you're happy with the new way.

(I'd define a working starter as one that has been successfully used to raise a batch of dough. Period.)