title: SCRUM estimation accuracy
body: <p>I would guess that there are a <em>lot</em> of cases where the estimation turns out to be wrong at some point. Because as soon as you drill down into the nitty gritty details of a backlog item you will probably almost always find something that you haven't thought about during planning. This can happen either during task level sprint estimation or during the actual sprint. </p>
  
  <p>During task-level estimation you might discover so many tasks for a story/backlog item  so that the initial estimation needs to be adjusted. 
  <strong>What do you do now?</strong> Do you go back to the product owner and tell him that he might want to re-prioritize its backlog items, now that takes much longer (or even less)? Basically it could mean that the whole team needs to go back to story-level estimation and reshuffle the stories?</p>
  
  <p>During the sprint you might discover that the implementation needs much more effort than initially thought. 
  <strong>What do you do now?</strong> Do you silently continue the sprint knowing that you can't finish it as planned? And from now on you will add a "security buffer" to all estimation?</p>
  
  <p>Generally, how does SCRUM address estimation accuracy as a whole? </p>
  
  <p>If I understood it right, the SCRUM developer team kind of "promises" the product owner that it will deliver as planned. But that can only be done if they estimated accurately. So estimation seems to be very crucial to the success of SCRUM but also very hard.</p>