A couple of days ago I read an article on Career Builder: The importance of life-long learning in the IT industry, by Scott Skinger. As the CEO and Founder of TrainSignal, it is not surprising that Scott is of the opinion that training is an important part of a long and successful career. Mind you, as the author of a series of certification guides, it is equally unsurprising that I am of the same opinion.
That said, anyone who spends just a few minutes thinking about it would be hard put to deny that being employed in the IT industry pretty much requires you to continue learning throughout your career. Most people have working careers that span more than forty years. How much 1973 IT technology do you think is relevant today? Which companies are looking to hire individuals with knowledge of it?
If you want to continue to have skills and knowledge that make you valuable to your current employer and interesting to prospective employers, you must continually learn and adapt to changes in technology. If you become expert in any given area and decide that you know enough, you will eventually discover your error. This may take years depending on how deeply invested companies are in the technology that you are expert in. Eventually however, something will come along to replace it. If you have established yourself as the 'Go-To-Guy' for the legacy technology, you will likely be tapped to maintain the legacy system until its replacement.
I am reminded of a quote from an old movie, Other People's Money. The main character in one scene says: "You know, at one time there must've been dozens of companies making buggy whips. And I'll bet the last company around was the one that made the best goddamn buggy whip you ever saw. Now how would you have liked to have been a stockholder in that company?" Do you really want to be the last employee at a company maintaining the code/system/application they are actively working to replace?
You should always be looking to learn new technologies and diversify your skills. This makes you look like a proactive employee and thereby adds job security. Having multiple different skills also reduces your chance of becoming obsolete. Even if one becomes less important over time, others should continue to be relevant.