as in “Nothing worthwhile was ever achieved without enthusiasm.”

It basically means that unless you are enthusiastic and passionate about what you are doing, you are less likely to see it through to the end—achieve it.

He saw the apple falling and discovered gravity.

He didn’t put any effort in making the apple fall.

The apple fell not because he liked and did something to make

it happen. was it enthusiasm.

Somehow, maybe a lot of men before him already saw an apple fell and yet they weren’t able to think of what newton discovered. Somehow when we were children we were able to an apple fell but we never thought that it was gravity making it.

All of us had opportunities tp discover it by ourselves but only newton showed enthusiasm on that simple thing that we never thought would become a great achievement.

Maybe enthusiasm is about grasping opportunities that will help us achieve things.

I hope my example helps you answer the question

RE:
what does this quote mean, " Nothing was ever achieved without enthusiasm"?

One needs excitement, intense emotions, even joy to do (achieve) something remarkable