If you think of computer applications as human assistants, interface design is easy to understand. You expect your assistants to see all your activities. In system designs, the ideal interface "assistant" is transparent, accessible, flexible, and task-oriented.
If you ask a human for a report, you expect to hear, "Yes," or "I am working on a current project now. I can have the report in 20 minutes. Is that OK?" But when you ask your computer interface to generate a report, you usually have to direct the system to the directory a needed file is in, access the directory, access the subdirectory, copy what you need, export it to a current working file, go to another directory and subdirectory to find more other bits of information, and so on.