It seems to me that our personal concept of God is a product of our culture, our family dynamics, our education, our life experience and our capacity to remain objective. Early man associated various gods with most natural phenomena; since then, as our species has evolved, our collective and personal view of God has become more refined.
Nevertheless, among modern human beings, there is a wide variety of beliefs, from a strict devotion to historical Scripture to atheism. The less we understand about the nature of our Universe, which may be due to the circumstances of our life or due to choices that we have made, the easier it is to retain a simplistic view of God.
In the end, regardless of ingrained beliefs and the level of our education, it is our determination and willingness to be objective that most influences our belief in a divine being. Were it left to the individual, this would be sufficient; unfortunately, devoutly religious groups in human society too often want to impose their beliefs on the rest of us.
See also: Man and Religion