Only then, with the reader’s attention "hooked," should you move on to the thesis.
To do this, it is a good idea to provide the reader with five or six relevant facts about the life (in general) or event (in particular) you believe most clearly illustrates your point. The importance of this step cannot be understated (although it clearly can be underlined); this is, after all, the whole reason you are providing the example in the first place.
For proof of this, consider examples from both science and everyday experience.
Because this is the first paragraph of your essay it is your opportunity to give the reader the best first impression possible.
You see, if your essay has the same structure as every other one, any reader should be able to quickly and easily find the information most relevant to them.
The principle purpose of the introduction is to present your position (this is also known as the "thesis" or "argument") on the issue at hand but effective introductory paragraphs are so much more than that.