System analysts wants the best fit and suited design.And when it comes to designing we want best possible use of people for designing computerized task which will fulfil organizational objective.The best fit mean better performance and good overall well-being for human involved in system.Users can be trained to develop a better fit and understanding by learning their tasks thoroughly.When the key performance is used in HCI context it refers to combination of efficiency required in completing a task and the quality of end result.For example if analysts is using high end software to create data flow diagrams in which they expertise then expectation is that quality of data flow diagrams produced would be high and performance will also be good as they are using familiar automated tool