wit's in a sentence

1. "We tend to see people who are at their wit's end—they've tried a number of diets and are severely overweight," Dr. Sha says.

2. I'm trying my best right now, but I am truly at my wit's end, and this whole experience has left me feeling more alone than I have ever felt in my whole life.

3. When I was finally at my wit's end and got tired of hearing people tell me there was nothing left to do, I had a friend of mine give me Doug Rutkowski's card and told me to give it a try.

4. If you are just plain sick and tired of being sick and tired and don't know what to do -- if everything you have done to help the alcoholic has only seemed to make things worse --and you are at your wit's end, divorce can seem like the only reasonable choice.