Power
Administrative assistants often have the most complete picture of how things work, and will have access to confidential information like employment files, legal documents, and salary information, that even some of the bigwigs won't see.
To wield that power, you'll need to be able to balance the needs of a lot of people in the organization making requests or even giving orders. The reality is that, without you and your filing and computer abilities, everything would crumble to dust.