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It's human nature that individuals and teams with self-esteem set increasingly higher goals for themselves.  And it's also human nature for teams to overreach their abilities, and they end either taking shortcuts to avoid disappointing themselves and their stakeholders, or fail to deliver what they expected.  By trying to achieve these goals, teams learn. Sometimes such strivings lead to immediate improvement, particularly when the team challenges itself to improve through use of a newfound technique or technology. Sometimes, however, the new technique doesn't pan out and the team's performance remains the same or even gets worse.
Sometimes, the team raises the bar just to raise the bar, either to test the limits or to unconsciously publish its bravado. These self-set performance challenges can pay off, especially in the short term. It is more common that these higher levels are unsustainable in the long term and performance reverts to original levels.
In some organizations there is pressure on teams to deliver more work than the team thinks they can commit to. The phrase “stretch goal” or perhaps “BHAG” (Big Hairy Audacious Goal) is the phrase used to make the amount of work seem exciting or challenging. Prescribing these targets on the team will crush autonomy and ignores the kaizen approach of the team that leads to greater work efficiency.
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The work will be properly sized for the upcoming Production Episode. The short-term average of the summed estimation points per sprint is called the Development Team's velocity. Since velocity is a statistical quantity with a mean and standard deviation, the team should expect about half of the Sprints to fall short of achieving Yesterday's Weather, and about half to exceed it. The goal is to improve the process to reduce the variance in the velocity, by reducing outside interference of the team, ensuring that the Product Owner provides Enabling Specifications, etc.
A notion of “use yesterday's values” was already mentioned in the 1980's  which referred to the forecasting research done by Spyros Makridakis and Michèle Hibon. This research is also known as the M-Competitions.
 Latham, G. P., & Locke, E. A. (2007). New developments in and directions for goal-setting research. European Psychologist, 12(4), 290-300. doi:http://dx.doi.org/10.1027/1016-9040.12.4.290.
 Ordonez, L. D., Schweitzer, M. E., Galinsky, A. D., & Bazerman, M. H. (2009). Goals gone wild: The systematic side effects of overprescribing goal setting. Academy of Management Perspectives, 23(1), 6-16.
 J. Scott Armstrong (1984). Forecasting by Extrapolation: Conclusions from Twenty-five Years of Research. In Interfaces, Volume 14, Issue 6, http://repository.upenn.edu/cgi/viewcontent.cgi?article=1083&context=marketing_papers, p. 12.
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