Many people that smoke want to give up. This is for a number of reasons.
Most of us realise that smoking is not healthy. It can cause a number of conditions such as cancers and blocked arteries, but it can also weaken the immune system and make the person more vulnerable to other illnesses as well. This is the main thing that is targeted at smokers, their health. However, unless we can see the health problems things are causing us, we tend not to take notice of them. We cannot see inside our bodies and it can take a very long time before we feel the effects of unhealthy behaviour and so this may not be a motivator. It is worth considering if you have children or plan on having them, that you will be likely to not only live longer but also be more able to do things with them, if you do not smoke.
There are other things about smoking which are not pleasant. The smell on the breath or clothing can be off putting. The staining on skin and teeth is also not pleasant as well.
The cost of smoking can be a big factor as the prices seem to be going up a lot and there are often tax rises as well. This money could be used for all sorts of things, saved up for a holiday, used to buy new clothes or nicer food. There are lots of possibilities.
Smoking is often used to reduce stress, but it actually makes stress worse in the long term. It is better to find an alternative way to wind down.
Smoking can also be unsociable and difficult. Now that you cannot smoke in public buildings, you have to go outside if you want one and it could be cold or raining. If you are having fun with someone in a bar, for example, you will have to leave them to go outside for a smoke. This is not much fun for either of you. Having to take smoking breaks at work could annoy people who do not smoke as they will have to continue working while you are outside.