This remark comes from Tony Hoare’s 1980 Turing Award lecture, “The Emperor’s Old Clothes”. He is describing how his team recovered from a failed software project by working in small, manageable steps and making no promises they could not keep.

The rule he singles out is that nothing was to be done that he did not himself understand. As the person responsible, he refused to approve any feature, design or schedule until its workings were clear to him. His two-word verdict, “It worked!”, records the outcome: deliveries met their dates and confidence gradually returned.

The point is both practical and cautionary. For Hoare, comprehension was a condition of control; what a leader does not understand cannot be reliably managed. The episode illustrates his wider conviction that clarity and restraint, rather than ambition or resources, are what rescue and sustain complex projects.

Full quotation

How did we recover from the catastrophe? First, we classified our 503 customers into groups, according to the nature and size of the hardware configurations which they had bought... We assigned to each group of customers a small team of programmers and told the team leader to visit the customers to find out what they wanted; to select the easiest request to fulfill, and to make plans (but no promises) to implement it. In no case would we consider a request for a feature that would take more than three months to implement and deliver. The project leader would then have to convince me that the customers’ request was reasonable, that the design of the new feature was appropriate, and that the plans and schedules for implementation were realistic. Above all, I did not allow anything to be done which I did not myself understand. It worked! The software requested began to be delivered on the promised dates. With an increase in our confidence and that of our customers, we were able to undertake fulfilling slightly more ambitious requests. Within a year we had recovered from the disaster. Within two years, we even had some moderately satisfied customers.