The retired high school principal addressed students at their graduation, spelling out the formula for success he had deduced from what students said whenever they came back to visit. "truly successful people," he told them, "are animated by hard work, dedication, and generosity." the general purpose underlying his speech is to

Celebrate.

Explanation:

The celebration of any events in the school can be done by addressing the students, motivate them by their speech and bless them to achieve success in their lives. This makes the student happy and feels the pleasure of joy and achieve whatever they want.

The principle that has been retired from schools has teach the student the formula to achieve success in their lives. The main purpose of this speech is he wants to celebrate the events at the school and makes the students feel importance in their life. This celebration feels the student with jeal and jest to achieve something in their lives.

Thus, the answer is celebrate.