These comments on the need to continually innovate raise the issue of sustainability of competitive performance SIA's rela tive to peers shows that it has achieved this, but what is it that makes it so difficult to imitate SIA? discussed below, it is easier to imitate fragments of a business system rather than the whole system if such a system is internally consistent and self-reiforcing held together by robust, customer-focused processes and the glue of cultural values, it becomes almost impossible to imitate.