Why Quantum Computers Repeat the Same Circuit Many Times

One execution produces one observed result

A diagram of a quantum circuit can look like an ordinary program that returns one definitive answer. Many quantum experiments instead estimate a distribution or a quantity derived from repeated measurements. A single run provides one observed outcome. Repeating the preparation, circuit and measurement provides information about how frequently outcomes occur under those conditions.

IBM's quantum learning material explains the probabilistic character of measurement. Its discussion of variational algorithms describes a sampler running circuits repeatedly and assembling a distribution from measured bitstrings. Those repetitions are commonly called shots. The terminology matters because a claim about the number of shots is a statement about sampling effort. It is not a count of different algorithms, and it does not by itself establish that the underlying computation was accurate.