This is a gross oversimplification, but you get the point. The scientists who cloned Dolly managed to catch each cell, the cell from the adult sheep's mammary glands and the egg into which they implanted the DNA, at the same exact stage of cell division. On the other hand, many proponents of cloning have suggested that it could have many beneficial uses, such as allowing infertile couples to have children that were genetically related to them. For example, the tendency towards introversion can be measured almost from infancy, before environmental factors have had much chance to influence personality. However, this genetic tendency doesn't doom one to a life of social introversion.
Many environmental factors come into play.
If, because of career demands, for example, the person feels a strong need to overcome his innate shyness, he can do so. Also, personality is subjective. Personality varies depending on who observes the individual. I was surprised at the outcome. My mother only rated me the same as I did 3 out of 4 times.