Expertise is more than meets the eye: One String IT Pieces
The "one-string piece" of IT (systems administration maybe) could be the various command line or Perl one-liners and what-not that does the job and astounds our bosses; where, as deadlines loom or we're in the middle of downtime costing the company, we pull out a one-liner that saves the day. Or it might even be the little things: the libraries or tools you've researched or played with in your spare time, and apply in a Eureka moment. You get that rush, knowing you've gotten the most bang for the buck, and your colleagues or bosses have no idea how you've accomplished so much with so little. Little do they know that you've been doing this kind of stuff for so long it comes naturally to you.
It can be the knowledge of various sed/awk/perl combinations that you've played with, then applied with awe-inspiring precision to the problem at hand. It can be the knowledge of the esoteric bits of the Java Language Specification or the Java memory model or even the class library, allowing you to figure out what exactly is going on underneath the hood, causing that heisenbug that your coworker has been debugging for days -- which you've solved in five minutes with a one line fix.
It could be that.
It's the stuff that others think they'd never really need, but you know will come in handy. It's the stuff that allows you to spend more time at the higher levels of abstraction, but with the knowledge that you're going to be comfortable going down to the bits and bytes if and when (most likely when) the time comes.
It's knowing that although GUI tools and wizards and nifty IDEs and autocompletion will probably cut down the time it'd take you to shape your code, you have to know how those tools work so that when it breaks you can fix it.