the original quote lost its full context and is giving the wrong meaning. knuth is trying to tell us to find joy in the most mundane things we do. he gave the example of cleaning the toilet, which his family does wearing suits.

solving top problems in quantum mechanics is, by any means, no mundane task.

but i have heard similar quotes before. about the joy of doing something being more important than the result. i think it's because joy is so contagious. shared joy makes you even happier, imo.