The single biggest challenge for project teams is scope creep. This is defined as uncontrollable changes or additions to the project's scope. Usually, this happens because the project wasn't clearly defined, or the group wasn't clearly communicating, or a bit of both.
Scope creep can have a detrimental effect on team interaction and project outcomes. Here is an example of what scope creep might look like in a project:
A company decides to build a mobile app so customers can purchase their products via their smart devices. The company isn't sure about all the specifics, but they hire a mobile app developer to help them design the app.
The developer conducts their assessment of what the company needs and begins work on the project. As they are working, the company starts sending over requests for new features they would like to see in the app.
At the end of the project, the developer delivers the app. The company isn't thrilled because the app doesn't work exactly...