But What if I'm Really Careful?
First, let's be clear. Anyone can sue you at any time for anything. Some file lawsuits because it's their only hope for paying their medical bills (remember the aunt who sued her eight-year-old nephew for breaking her wrist?).
Others might sue at a lawyer's insistence. For example, if a drunken party guest has a car accident on the way home, the damage they cause may be your responsibility. This is called host liquor liability, and while a lot of homeowners don't know about it, most lawyers do.
Other lawsuits are frivolous through and through, but you still have to respond to them and pay for your defense.
Long story short? You don't have to do anything wrong to find yourself embroiled in a costly lawsuit.