How difficult is it to be a staff in the same institute?

Hi all, I have just started new postdoc at one of US national laboratories. It has been a month, and I like this laboratory. It treats their employees very well, and I had freedom in making decisions in my projects. I just saw the statistics from postdocs in this laboratory, and 39% of postdocs are promoted to staff. Is it difficult to be promoted to staff in a same laboratory after completing postdoc?