The best answer I had was towards some work colleague who has seen me around rather frequently at the customer site and he asked me what I'm doing here.
My first answer was a classic one: "I work with computers and most of the time around databases." - Nice try, wasn't it? Well almost:
"What do we need you or databases for?" This got me a little bit thinking and I told him "Well, you probably know this better than me but I've been told you're struggling every year ordering the perfect required amount of tyres for your customers once winter season begins, right?" "Oh yeah, we definitely struggle with that every year!" "Well I'm building data so you'll hopefully be able to order the right amount of tyres at the perfect time of year for that in the future."
"OK, this really sounds useful."
There we go, I sometimes have to do a "triple double step-back" in order to explain what I do to someone in a meaningful way, too but usually people at least believe to see I'm doing an important job in some way.
But to answer your question: What keeps me in my job mostly asides having some years of experience in very large organizations will be my honesty: I do not fear at all to talk to the customer where I think his problems come from - as I have 5+ years experience in performance optimizations, everyone I come to in some sort of way has performance issues with some DBs - and the last thing I fear to call out either code or HW sizing "failures" at layer 8.
I think this provides much more value to my customers than just those few lines of SQL Code and SSIS GUI drawings I might do on the sideline, too.