In the rapidly changing new world, you've got to abandon the linear career trajectory.

Instead you should get comfortable with the "squiggle," argues digital marketer Mitch Joel in his new book, "Ctrl Alt Delete." That means being ready and willing to adapt to new challenges and opportunities.

In practical terms, Joel offers four lessons from a squiggly career, which we've summarized below.

1. Don't be afraid of short and powerful projects.

You should be "constantly working to put ideas, innovations, and products into market." This could involve multiple projects within an organization or working with multiple organizations. Switching jobs won't hurt your resume as long as "you can prove that the moves you've been making were done because you accomplished (and surpassed) the pre-established goals.

2. Don't be afraid of big.

"If you're not thinking about the bigger problems that face your industry, someone else is," Joel writes. As examples of people who dreamed big, he cites Jack Dorsey, who dreamed of a world without cash registers, Steve Jobs, who talked about making a dent in the universe, Mark Zuckerberg, who talks about connecting the world, and Sergey Brin and Larry Page, who talk about organizing the world's information. Big dreams are within reach these days.

3. Get Squiggly.

This means not getting stuck in "decisions that you made and followed back in high school and university (or because your predecessor did things a certain way)," Joel writes. Be willing to switch to a totally new career. Even in your current job you can "take on a challenge within your organization, work with a new department, change something within your business that is antiquated or draconian."

4. Be incompatible (maybe just a little bit).

What Joel means here is that you have to be willing to be unpopular, as you will be if you push for change, make people do things they don't want to do, treat your work like art, disrupt the way other people do things, and commit to lonely work. "

"Ctrl Alt Delete" is a reassuring book for millennials, who have been criticized for their inability to commit to a steady job, and also for older workers, many of who have watched as their industry has imploded in the IT revolution. Not everyone is going to be the next Steve Jobs, but an openness to change is a useful attitude change.