A person buys a sports car and then, rather than admitting that the decision was based on a desire to look youthful and attractive, starts chatting about the car's great mileage.
As the marketing folks say, we tend to buy on emotion and then justify our decision with logic.
Interpersonal relations are hardly immune from such games. Individuals may say that an advisor or ally is necessary to prevent lawsuits or facilitate good management but the real reason for the relationship is simple: People want to look good and the source that assists in doing so is both helpful and appreciated.
I know the power books urge people to grab credit in order to avoid being exploited but you can gain a great deal - both internally and externally - by helping others do well. When they succeed, rather than trying to parse the extent of your contribution so you can get your just due, it is often wise to stand back and let the other person get the applause.
Is this naive? Many would say so. My take is that you can gain a great deal of personal satisfaction in the process making others look good and, over time, people who don't constantly keep score of "Who owes them what?" have a habit of getting promoted.