In a nutshell

Tuckman demonstrated that when you bring a group of people together they are likely to go through several stages of development before they become a high performing team. The stages are:

Forming – the group comes together, but isn't a team

Storming – just starting to get to know each other better

Norming – beginning to work together

Performing – working together really well

On top of this, teams rarely remain unchanged. As people leave the team there will be a certain amount of mourning for their loss, and as new people arrive there is likely to be a certain amount of norming and storming before the teams is able to perform at its optimum.

Disciplines that help the team understand its purpose, and how each person can contribute, can help the team form and help prevent storming. This is one reason why a product vision and roadmap are so important, and why involving the team in planning activities is vital.

Disciplines that help team members understand each others needs and strengths are likely to help better norming, and reduce storming. This is one reason regular stakeholder reviews and retrospectives are essential.

A Team Charter can be used to capture how the team wishes to operate and can help the team align to its purpose throughout every stage.