It is fear that you will not be able to enjoy coffee (or alcohol) or handle stress. Fear that you will put on weight. Fear that you finally will not get free of the desire to smoke. Fear that it is just going to be too painful and too difficult.
Maybe you have heard that the sudden cessation of smoking (cold turkey) can do all sorts of dreadful things to the body. There have never found a piece of evidence to support those claims. It is absurd idea. Quitting smoking can bring nicotine withdrawal symptoms. Those symptoms include poor concentration, petulance, impatience, food cravings, and lots of other. Remember they do not last too long, but you get advantages for the rest of your non-smoker life, because quitting smoking lessens the risk for heart problems, getting lung cancer, and other fatal illnesses.
Surely, it is difficult, but extremely possible, to quit smoking and not everyone gains weight when they stop smoking. The benefits of quitting begin almost immediately and continue to increase over time. If you smoke long time, you also get the benefits of quitting smoking quickly . . . and for the rest of your life. It is never too late to benefit from quitting smoking. Remember that smoking is the problem - a costly, stinking one that causes nothing but harm to our lungs and bodies. Smoking does not help find the solution to any problem, but quitting smoking is. There is no reason to ignore that smoking never did anything positive for you. Quitting smoking takes hard work and a lot of effort, but you can quit smoking.