Mission creep

Mission creep is when a project or task starts out with one plan, but then slowly changes into something bigger. For example, say a group of friends starts cleaning up a messy room. At first, they agree it will be a quick job, but as they start tidying, they decide to rearrange the furniture and give the walls a new coat of paint. This is mission creep because the project kept growing until the group was doing more than originally planned.