The accident that saved a hundred million lives.

In 1928 a Scottish bacteriologist named Alexander Fleming returned from a summer holiday to a laboratory he had not bothered to tidy. Among the dishes of bacteria he had left out, one had been contaminated by a stray mould, and around that mould was a clear ring where the bacteria had simply died. A tidier scientist would have thrown the dish away. Fleming looked closer.

The mould was producing something that killed bacteria, and he called it penicillin. For over a decade it remained a curiosity, difficult to produce in any useful quantity, and it took a team at Oxford, led by Howard Florey and Ernst Chain, to turn Fleming's observation into a drug that could be made at scale and put into a human arm. By the Second World War it was saving wounded soldiers who would previously have died of infected wounds rather than the wounds themselves.

It is hard, now, to feel how total the change was. Before antibiotics, a scratch from a rose thorn could kill you. Pneumonia, childbirth, minor surgery, a cut that turned septic, all routinely fatal. Penicillin and the antibiotics that followed pushed those deaths off the table so completely that we forgot they were ever there. The estimates run to hundreds of millions of lives saved.

Two things make the story worth keeping. The first is the role of the prepared, curious mind. The contamination was luck. Noticing what it meant, and refusing to dismiss the anomaly, was not. The second is that Fleming and the Oxford team declined to patent penicillin, believing a medicine that could save so many should belong to everyone. It was given to the world.

For anyone who makes or discovers anything, the lesson is to respect the anomaly, the thing that went wrong, the result you did not expect, the mess you were about to clean up. The most important findings often arrive disguised as mistakes, and the whole game is being awake enough to notice.

What went wrong in your work this week that you were too quick to tidy away?