Ask HN: Mathematical discovery as a slow plodding business

I'm looking for a PDF of an essay / paper written by a maths professor which characterised problem-solving in maths as a matter of persistence rather than genius. It was posted here about 6 months ago. Does anybody remember the link?

The author explained that he was not particularly intelligent, but had done his best work by spending lots of time on particular problems, rather than through sparkling insight or special talent.