Especially for young people, the amount of time that you have been alive is small compared to your lifetime. What you currently know to be interesting is correspondingly a small subset of the number of things you can find interesting over a lifetime, and an even smaller subset of the things which you could find fulfilling to work on with many lifetimes. (For those who have lived longer, your life experience makes it even more likely you can identify fulfilling connections/facets of the universe to study.)
The challenge is to find the intersection between what you can be riveted to work on, and what society values (in whatever its flawed wisdom) or can be invited to value. This is not trivial, but the statistics of the universe are on your side.
What sort of society would we be if e.g. Nikola Tesla/Jame Clark Maxwell/Mozart/etc. had followed this advice?
To aspire is human, powerful, fulfilling. To eat is practical. It is possible to do both. Society needs people who persist in that pursuit.