Most people try to quit smoking several times before they kick the habit for good, so don't beat yourself up if you start smoking again. Turn the relapse into a rebound by learning from your mistake. Analyze what happened right before you started smoking again, identify the triggers or trouble spots you ran into, and make a new stop-smoking plan that eliminates them.
It's also important to emphasize the difference between a slip and a relapse. If you slip up and smoke a cigarette, it doesn't mean that you can't get back on the wagon. You can choose to learn from the slip and let it motivate you to try harder or you can use it as an excuse to go back to your smoking habit. But the choice is yours. A slip doesn't have to turn into a full-blown relapse.
Having a small setback doesn't mean you're a smoker again. Most people try to quit smoking several times before they kick the habit for good. Identify the triggers or trouble spots you ran into and learn from your mistakes.