The answers are : 1. Family use 2. Weight loss 3. Celebrity use 4. Peer pressure
1)Family use is a personal reason. There are studies that say that children of parents that smoke are way more probable to be smokers to. That's because the parents are reacting to smoking as a socially acceptable behavior.
2)Weight loss- In some people, smoking makes people lose weight. Someone who maybe is trying to stop smoking, when they see that they are gaining weight, makes a compelling reason for them to keep smoking.
3. Celebrity use: social influences can also exist by celebrities.Movies, advertisements, etc, can make a celebrity look cool and attractive while smoking, making it appealing for teenagers that admire those people.
4)Peer pressure is one personal reason because people start experimenting with tobacco, usually when they are teenagers and they don't want to be alone, or they don't want to seem they are weak and afraid.
Another example of a personal reason would be stress.