mainly (though not exclusively) because of nicotine that highly stimulating substance naturally found in tobacco, which is associated with the pleasurable, euphoric feeling, which also makes smoking so incredibly addictive
In these cases, doses should be kept low and be administered intermittently (gum) rather than constantly (patch)
I hope the ideas shared above have given you some inspiration of what habits to try and replace smoking, with as well as a deeper understanding of how to implement behaviour change effectively
That said, these changes are often modest and can be influenced by other factors that often happen after quitting smoking, such as changes in diet, appetite, or weight
If the person is between outbreaks, asymptomatic shedding makes the risk low but not zero