If you've been hanging around computers as long as I have started working on them in the late 1970s, bought my first one for home use in the middle 1980s you're acutely aware of the fact that your learning curve never bends back down toward the x-axis. There is always more on your plate, and barring the world's largest electromagnetic pulse or the reincarnation of Ned Ludd, there's always going to be more on your plate; you can't possibly stay caught up for more than a few seconds before something new comes along.
And this is true even if you work on something fairly established. I've toiled for the better (or the worse, depending on the mood of the moment) part of two decades on IBM midrange systems, from the old System/36 through various AS/400s to the current System i, a market which might be fairly characterized as "mature": its current users are loath to leave certainly we're not going anywhere but the growing-like-a-weed pattern you see on other platforms is conspicuous on the i by its absence. IBM, sensibly, has chosen to beef up its software offerings by going to the open-source well. (Our corporate Web server, which runs natively on i5/OS, is good old Apache.) This push into open source, however, means that those of us who work on the i can't afford the luxury of complacency between i5/OS release versions: we have to keep an eye on whatever might be happening across the county over in Un*xville.
This concentration, though, coupled with massive changes over on the microcomputer side of life, has meant that I've fallen grievously behind in my PC prowess: I no longer feel competent to assemble a working box from a drawer full of spare parts, something I used to do almost routinely. Were this part of my job, I'd fear being replaced by someone younger, perhaps more efficient, certainly with fewer skinned knuckles. Fortunately, said someone is already on site servicing workstations, and we get along just fine, since (1) I don't pretend I know what I'm doing 24/7 and (2) it's wholly unlike me to play the Guy Card: I learned many years ago