Reasons could be:

• Scrum team doesn’t trust the scrum process and feels pressurized every time.

The Product Owner and Scrum Master should ANALYZE the issue and discuss with each team member individually or in RETROSPECTIVE meetings. Make them understand the Scrum process and encourage them to again trust their process and their own estimates.

• Lack of clarity of user stories.

There are scenarios where a team doesn’t have any clarity on user stories, as a result of which they add more estimates to the user story during the sprint planning meeting. The Product Owner and the team should own the responsibility of getting the clarity of user stories. The team should ask as many QUESTIONS as they can to start work on the user stories.

• Field issues or other unplanned work

Sometimes the team is working on current sprint but there is unplanned work which might come as the same team is working on the same. Ideally, it should not be but have seen this practically.

• User stories have technical debt

User stories have some technical debt example technology not defined, database storage etc. during implementation which tools to be used. In these conditions team sometimes estimate higher. The solution could be these could be treated as part of Definition of Ready state or take them as a spike user story.

• The team is not experienced in estimating stories

When a team moves from the waterfall model to the scrum process, they MAY estimate it higher as they are new to the process. Training on Agile estimation techniques will be helpful.

• Dependency on other activities

Sometimes the team may estimate higher thinking that to do one PARTICULAR task there is a dependency on other team or some vendors.  Example-Purchase of hardware or License to some tool which is used for development etc.