Disruption

A new entrant serving the least profitable customers with a cheaper, initially worse product, then improving until it takes the incumbent's core.

The word is used loosely for any change, which drains it of meaning. The specific mechanism matters: incumbents lose not because they cannot see the threat but because responding to it means abandoning their most profitable customers, and every rational internal process argues against that.

The diagnostic questions are whether the entrant's product is worse on the dimensions incumbents compete on, whether it is improving faster, and whether the incumbent's own economics prevent a response.

Most competition is not disruption. Some is, and it is fatal.