The two mistakes
Answer it in your head first.
You are weighing up whether to see a doctor when the family is sure this is affliction. What are the two possible mistakes, and are they the same size?
One mistake is going to a doctor when the cause was something else. The cost of that is an appointment and an afternoon, and the recitation carries on the whole time. The other is waiting when it was a treatable illness, and the cost of that is measured in months and years. They are not the same size, and that is the whole reason to act on the second question first.