Software cannot be inspected like shipbuilding or a civil engineering project in which it is visible which parts of the structure is unfinished. Software is intangible. That means, it cannot be seen or touched.
Some of the important goals of software management are delivering the software in the proposed time, budget and to meet all the requirements of the customer. But the software being intangible, it is difficult for the software project managers to tell exactly what the status of the development is. They cannot see the progress by simply looking at the artifact that is being constructed. Rather they rely on others to produce evidence that they can use to review the progress of the work.