I'm not sure that's good advice. 80,000 hours has given pretty good arguments against just "doing what you're passionate about".

Passion grows from appropriately challenging work. The most consistent predictor of job satisfaction is mentally challenging work (2). Equating passion with job satisfaction, this means that we can become passionate about many jobs, providing they involve sufficient mental challenge. The requirements for mentally challenging work, like autonomy, feedback and variety in the work, are similar to those required to develop flow. This suggests that a similar conclusion will hold if we believe that being passionate is closely connected with the ability to enter states of flow. If, however, you don’t think flow and job satisfaction are the same thing as passion, then you can still agree that…

There are better targets to aim for. We’re not only bad at predicting what will make us happy, but more easily detectable predictors of job satisfaction exist (autonomy, feedback, variety, making a difference etc). This suggests it would be more useful to aim at these predictors rather than directly at what we think we’re passionate about. Similarly, it could be more useful to focus on being good at what you do. First, this is a more positive mindset, focused on contributing rather than taking. Second, being good at what you do makes you better placed to ask for engaging work.

Related: http://80000hours.org/blog/63-do-what-you-re-passionate-about-part-2