The reader needs to know this and it is your job as the writer to paint the appropriate picture for them.
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.
Following the thesis, you should provide a mini-outline which previews the examples you will use to support your thesis in the rest of the essay.
Not only does this tell the reader what to expect in the paragraphs to come but it also gives them a clearer understanding of what the essay is about.
Finally, designing the last sentence in this way has the added benefit of seamlessly moving the reader to the first paragraph of the body of the paper.
In this way we can see that the basic introduction does not need to be much more than three or four sentences in length.
Try instead to be more general and you will have your reader hooked.
The middle paragraphs of the essay are collectively known as the body paragraphs and, as alluded to above, the main purpose of a body paragraph is to spell out in detail the examples that support your thesis.
Only then, with the reader’s attention "hooked," should you move on to the thesis.
The thesis should be a clear, one-sentence explanation of your position that leaves no doubt in the reader’s mind about which side you are on from the beginning of your essay.