In past generations people went to work for a company, stayed a lifetime and enjoyed job security.
Today, you are responsible for your own job security. No matter what your position, you cannot assume that your job is safe, or that the company is stable (including government jobs). So you need to prepare, even when you are employed.
Since many experts agree that more than 70% of jobs are found and filled through networking – creating and maintaining a network will be vital, so you can quickly find new employment, or new opportunities. (The reason why networking works, is because a typical employer prefers to hire someone that is known through a network, or someone that comes recommended by a friend or colleague. Job boards are used as the last resort, not first resort by employers).