An effective introduction usually tries to capture a reader's interest. This is because the introduction is the first part of the text that the reader will read, and this will influence whether the reader continues reading the rest of the text. Many strategies can be useful in capturing a reader's attention, but two of the most important ones are asking a question that leads the reader to reflect on the topic or providing an interesting fact about the subject.
The last paragraph explains that too many false alarms can be dangerous to one's health, which is important to explain since the rest of the passage seems to promote stress as a way to survive or thrive in moments of crisis.
