What does "nothing unknown" mean in this quote?

I am reading a book which contains the following quote by Johann Wolfgang Von Goethe at the beginning of a chapter:

For him who seeks the truth, an error is nothing unknown.

What does it mean? In particular, what does "nothing unknown" mean?

For those who are curious about the context of this quote, it is in Chapter 5 "Randomized Algorithms" of the textbook "Algorithmics for Hard Computing Problems" by Juraj Hromkovič, and randomized algorithms typically allow the possibility of making mistakes as long as the error probability is small enough.

It would appear to be a way of saying that

Those who seek truth are accustomed to making mistakes in the process.

The double negative construction of the original is familiar to educated English speakers (especially Britons and scientific writers) as a way of softening an assertion. The use of “nothing unknown” rather than direct statement is also literary. It conveys a certain irony or philosophical generality.

As the original German is by Goethe, this style can be regarded as appropriate.