Although success can be measured in many different ways. Beetles are incredible successful if you count success in terms of number of species, and I doubt they have 5 fingers.

No, I'm talking about vertebrates only.

Quote - The other lineages died out, and the one that was left just happened to have five digits on each limb.

This to me contains basically the same information.*

Not to me.

There were creatures with different numbers of fingers. Some of them died out and some of them didn't. The 5-fingered line continued. Personally, from my own POV, I'd count that as successful compared to the lineages that died out ;)

But it's not the fingers that made the difference. This is shown by the number of vertbrates today that have a different number of digits, such as pandas and horses. Five is not naturally the best. It's just a leftover, like the human appendix and tailbone.

Sorry, but this is a pet peeve of mine. People tend to interpret evolution as "whatever is, is best." In fact, it's the opposite. Whatever is, may be just an accident.