Why Dev estimation is a Chink in sprint planning's Armour?

 Never assess the piece of work from the eye of strong technical developer. It is not right do so. Why? Let say your strong tech guy estimate for 2 days whereas your in general rule of thumb says otherwise then there is a major fault. On the contrary , team needs a buffer there is so many unforeseen contingencies that never cater to. Whether it is dev or testing or any other areas we must understand to factor many aspect such as resource time off, discovery, impact analysis , proof of concepts , dependencies and other caveats. Well the estimation is a key driver to set a right expectation and align budget costing model to its right dimension. We should set the delivery compass such a way it will steer us in a right direction.