If someone works with a piece of software every day, they're going to start navigating it by the position of elements in the software, not what the text around

If someone works with a piece of software every day, they're going to start navigating it by the position of elements in the software, not what the text around the elements say. If the "erase form" button was placed below and to the right of a web form, where the "submit" button usually is, you bet it would cause a fair amount of swearing. If the doctor is used to working with older/larger patients (over 40kg) they might get that screen only rarely, and perhaps because the patient was so close to 40kg, she wasn't thinking in "pediatrics" mode, and expecting it to come up.