My first son was addicted to his pacifier. If we fed and changed him and he was still upset, it was the only thing that would calm him down. The sucking action soothed him. We joked that the paci was like his mute button. But every so often in the middle of the night, it would fall out and then you guested it - he would cry! We found ourselves getting up repeatedly to plop it back in.
Flash forward to my second baby, who is a self soother. He sucks on his two middle fingers instead of a pacifier. He never took a paci, he only used his fingers! In fact, I have an ultrasound pic of him doing just that. Sometimes I can hear him going to town on his fingers in the middle of the night.
It's just amazing how different two children can be, even at such an early age.
One thing is for sure, I had to break my first son of his pacifier so I'll have to do the same for my second son (only with his fingers)!