What metaphor does Tony use, to describe his relationship with Sal O’Nally?

Tony says that he has climbed a ladder with Sal’s assistance, but that now that he had accomplished his rank, he does not need the help any more. He muses, “What use is a ladder, once you’ve climbed it? You kick it away, if you don’t intend to go down it again” he considers whether to throw his support behind Sebert instead of Sal (211).