Existentialism discussion

I know that Beckett is not really an existentialist but I have this project: I was asked to create an illustration based on Beckett's quote "Try again. Fail again. Fail better." by using a relevant text. Now I was supposed to pick a side (about how that is a positive or negative quote) but to be honest I consider this quote to be entirely subjective. So, I would be much obliged to anyone who can offer me an idea of a piece of text that relates to the subject of trying and failing or of evolution and human nature in general and how we truly evolve or not. Thank you very much in advance.

Here's an idea:

“Progress has not followed a straight ascending line, but a spiral with rhythms of progress and retrogression, of evolution and dissolution.”

--Johann Wolfgang von Goethe

That is so good! Thank you very much! It's very close to what I need. I found the rest of the text and it is very helpful, thank you so much!!

Thank you very much for your replies! In the end I needed more than just a few quotes so I linked Beckett's text with text from "thus spoke Zarathustra". It contains many of the ideas I needed and the professor is pleased so yay :)