There are benefits of presenting yourself as an expert. Confidence in your knowledge affords you respect from peers and clients alike, but it's more important to stay humble and never stop learning.
It's true that clients should be able to trust you, and it helps when you present yourself as an expert. However, the only way to stay relevant in an evolving industry is to keep learning.
In my programming class, Mike Robinson (the instructor) told us, "If you don't like reading about this stuff, this isn't the field for you." To paraphrase the rest of his sentiment: "young kids" are coming into this field and getting all the jobs because companies want programmers who are relevant, who know the latest versions of the languages, and who are ready to keep learning as technology keeps evolving.
What you know now may not be so valuable down the line -- after all, technology and everything it touches keeps changing. It's important that you hold onto your inner student, and even when you're presenting yourself as an expert to your clients, you continue to do what students do when clients aren't around: pick up a book, take a class, and ask questions. And, of course, this goes for more fields than just programming -- it goes for all of us.
Find out what kind of knowledge is in demand by grabbing a copy of the course catalogue from your favourite university. If you see something your future replacements are learning that you aren't familiar with, get familiar with it to stay relevant even longer.
Picture: Lidyanne Aquino/Flickr