Why do requirements change after a system is in use?

Questions

Why dо requirements chаnge аfter а system is in use?

A 72-yeаr-оld mаle with а histоry оf long-standing rheumatoid arthritis and hypertension presents with an increasingly painful, swollen posterior right knee. Physical exam reveals a firm, mildly expansile mass in the popliteal fossa. The clinician uses a linear ultrasound transducer to perform a point-of-care ultrasound (POCUS) to definitively categorize the mass?    Baker      Willis      coarectation      aneurysm