Mark Twain once said, “It's easy to quit smoking. I've done it hundreds of times.”

Many ex-smokers say that quitting was the hardest thing they have ever done. If you have tried to quit before, you know how hard it can be. While millions of people have successfully quit smoking, it’s still important to acknowledge that quitting can be difficult. And here's why....

Smoking is a nicotine addiction - as addictive as heroin or cocaine.

When you smoke, nicotine reaches the brain in about 10 seconds. This causes a chemical called dopamine to be released in the brain, providing feelings of pleasure. Over time, more nicotine is needed to reach the same level of pleasure. The more you smoke, the more nicotine you need to feel good.

When you stop smoking, your body reacts very quickly to the lack of nicotine in your system, and you will likely experience a number of withdrawal symptoms that will urge you to smoke again. The urge to smoke can be very strong and there are a number of factors that cause this urge:

Brain chemistry: Nicotine is a very powerful drug that affects mood, focus and thinking. In seven to ten seconds after a puff of a cigarette, nicotine begins to calm a smoker’s brain. The brain gets used to hundreds of nicotine ‘hits’ each day, one with each puff.

Behavioural conditioning: Smoking is driven by stimulus-response behaviour. For example, the smell of a cigarette or a cup of coffee may produce an automatic urge to smoke for some people who smoke. A lot of smoking is done automatically, without thinking about it.

Psychological: People who smoke often feel they need a cigarette to help them deal with stress or feelings such as anger or irritability. People with a family history of depression, schizophrenia, attention deficit disorder and other conditions may have an especially hard time stopping smoking.

Social Aspects: Smoking is a social ritual for many people, shared with family, friends or co-workers. When other people light up, it is often natural for the person who smokes to join them. This is doubly challenging for those where everyone in their social group smokes.

There are more people who are ex-smokers than current smokers.

The good news is that nicotine addiction can be overcome. For some smokers with low levels of addiction, quitting may be relatively easy. But for many others, quitting for good, or reducing the amount you smoke may take several attempts before you succeed.

Learn how addicted you are so you can make a quit plan that will work for you.

View video developed by the Mayo Clinic on why quitting is so hard.