Research on infants finds significant differences in various measures of temperament at birth. Your young one brings his or her personality into this world. But enough about science. I want to tell you about my experience.
I had twins. Well, actually, my wife had twins. But I helped.
And once we had them they were beautiful and amazing and life altering. But they were also very difficult. My mom lived with us for a month to help out. She had three kids herself, so she had some experience in the matter. She loved her grandkids passionately, but she was struck by how difficult they were. They had colic and they both cried a lot. And I mean a whole lot. Especially in the evening.
They would begin crying around 6:00 p.m. and they were barely consolable. I would get home from work, eat, and then would spend the rest of the night holding them, rocking them, swinging them. We read about colic and tried everything. It helped, but they were nonethless very difficult.
Then, just as the books told us, around six months or so, they started to improve in their temperament. My son in particular continued to have difficulty with being over-stimulated, but things just steadily got better and better and better. And it didn't stop. Every year was great, but each new year seemed even better. They were both wonderful children. Great in school, loving, helpful around the house, inquisitive, intelligent and fun. They were everything a parent could wish for in a child, a blessing in every way. I have concluded that my children were born with some neurological wiring that made them particularly sensitive to sensory stimuli. With love and support their sensory sensitivities morphed into artistic and emotional sensitivity that makes them wonderful, responsible, loving humans.
So if you have a difficult child, read up, figure out what you can do, get support--I know how overwhelming it can be--but hang in there. Even difficult babies can turn into wonderful beings with your love and patience.