A USA TODAY Snapshot looks at why smokers find it difficult to quit. Twenty nine percent of the respondents said they haven't been able to quit because of stress.

The survey also found that 12% of respondents couldn't quit because they enjoyed smoking, and another 12% said the cravings were too strong.

Other reasons included weight gain, addiction, and smoking friends or spouse.

Ex-smokers average nearly 19 years and 11 attempts before they can quit.