A PhD topic is like a relationship, so you need to take care when deciding on one, writes Cindy Duarte Castelão at Bitesize Bio.
And it's going to take a lot of your time and energy. "Think about what you really, really want to do," she says. "Don't get yourself into a four-year relationship if you don't see a future in it."
The best time to figure out what you like and what you want to do is before even entering graduate school by spending some time in a lab as you want to be sure you like it there. Duarte Castelão also says not to be swayed by the latest darling topic — and the funding lavished on it — if it doesn't interest you at all. "[R]emember that you are stuck with your subject for at least 4 years," she writes. "That is a lot of time to have something on your mind 24/7, if you don't really love it."
At the same time, she notes that nothing is forever. If you wind up not liking your topic, you can power through and transition to another field once you've finished or even can walk away.
"Nothing is set in stone, and we can always find out what we really love to do," she says. "It is never too late."