What is the topic sentence of this process paragraph?

Sentence $7$: However, the fourth misstep that leads to foreclosure is when homeowners postpone seeking assistance until their legal rights have passed, or they walk away from their homes without retaining any of their investment.

Sentence $2$: The first event leading to the foreclosure process involves the home purchase itself, specifically buying a home beyond what the buyer can comfortably afford.

Sentence $1$: Although the foreclosure crisis has been covered extensively by the media, many people need to know the events that they need to avoid in order to avoid foreclosure.