When Weil asked him
which work of his he thought best, he replied,
“Oh, I think a few watercolors I made in Greece
some years ago are pretty good.”

https://www.ams.org/notices/199611/comm-steele.pdf

*One professor began to laugh at me. Each time we met he would ask: "Have you proved the unsolvability of Hilbert's tenth problem? Not yet? But then you will not be able to graduate from the university."*

Eventually he decided that he would have to forget about Hilbert's Tenth Problem and concentrate on other problems for his Candidate's Degree. However:-

*... one day in the autumn of 1969, some of my colleagues told me, "rush to the library. In the recent issue of the Proceedings of the American Mathematical Society there is a new paper by Julia Robinson!" But I was firm in putting Hilbert's tenth problem aside. I told myself, "It is nice that Julia Robinson goes on with the problem, but I cannot waste my time on it any longer." So I did not rush to the library. But somewhere in the mathematical heavens there must be a god or goddess of mathematics who would not let me fail to read Julia Robinson's new paper. Because of my early publications on the subject, I was considered a specialist on the tenth problem, and so the paper was sent to me to review. Thus I was forced to read Julia Robinson's paper, and Hilbert's tenth problem captured me again.*

https://mathshistory.st-andrews.ac.uk/Biographies/Matiyasevich/