Karp versus Spielman

Some years ago, Dick Karp told me that he only worked on "easy" problems.
Last week Dan Spielman told me that he likes to work on "hard" problems.

Some years ago, Dick Karp told me that when he almost never got stuck on a
problem; he never worked on a problem unless he had a way forward. Last week
Dan Spielman told me that he was very stubborn, having a hard time
abandoning a problem.