An experiment that fails still answers a question. It just wasn’t the answer you were rooting for.

Disappointment and uselessness are not the same thing; a result you did not want has still removed one possibility from the list. The disappointment comes from having been attached to an outcome, which is a separate matter from whether the work told you anything. Most progress is made of narrowing, and narrowing feels like very little at the time.

Write down what you expect before you run the next experiment so the comparison afterwards is honest. When it goes the other way, record what is now ruled out. That sentence is what you actually earned.