A few years ago, I went to a public interview/chat with Rainer Weiss in NYC. He described years of work in which the LIGO team found inventive ways to make their systems more precise. They just kept knocking down orders-of-magnitude. Still, after taking new measurements, they found nothing. No gravitational waves. Then the interviewer asked him if he was discouraged at this point in his career. I loved his response. He said, "No, it was a more meaningful zero."