Nicotine boosts adrenalin and a host of other chemicals, increases blood pressure gives you something to concentrate on. The downside is it rids you of the ability to relax for long periods. Your brain becomes used to the artificial hormone imbalance, you develop the need to keep the plates spinning, and you can't relax for long without the need of a cigarette arising. In the end, how could an artificial tampering of your neurochemistry via 4000 chemicals in smoke compete with millions of years of evolution? You don't need cigarettes to stay alert, you need some excitement, some motivation, and some constructive goals. Nicotine is the last thing you need.