Because one may learn that those fears are overblown. Or they may learn that they cannot build any kind of software without reviewing every line of code.

The person is saying "I am still unable to stop" and that is most likely because they feel a sense of responsibility. If they choose a project where there is no responsibility, where it literally doesn't matter if the project fails, they may feel able to stop. And if they manage to make that project work, if they can succeed, then they will build up confidence.

It seems better to be able to work both on projects where they review all code as well as projects where they do not review any code. In fact, keeping their job in the long term may (or may not) require having both skills.