In 2011, the language of the Scrum Guide changed:
One of the most controversial updates to the 2011 Scrum Guide has been the removal of the term “commit” in favor of “forecast” in regards to the work selected for a Sprint. We used to say that the Development Team commits to which Product Backlog Items it will deliver by the end of the Sprint. Scrum now encourages the Development Team to forecast which Product Backlog Items it will deliver by the end of the Sprint. It may seem to be a simple wording change, but in fact there are strong reasons behind it, and surely it will have great implications.
Years earlier, Eli Goldratt in one of his recorded lectures noted:
Treating estimates as commitments for complex project work is in conflict with the desire of the individual to be seen as a reliable person.
This behavior destroys:
- Morale/Transparency
- Quality
- Forecast Accuracy
[Special thanks to James Carpenter for transcribing/paraphrasing Goldratt’s lecture.]
noestimates.wordpress.com 
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