Pure dread, when you have signed up for a new gig and open an existing code base for the first time. Starring at hundreds of unknown files and folder with no idea what anything is and how it all works. No going back, you're a new maintainer, so better get to it. Usually after a few days you start getting a grasp, and it's not so bad though :)
A few days is exceptional. On average it takes me 3 months to a year to get to a point where I even kinda sorta feel comfortable in a codebase. There have been exceptions, but normally I find they're just written very expediently.
Feeling the same still after a few months. And dread is not very helpful when someone asks you to implement the new feature "now" (like none of your current tasks are as important as reducing the number of decimal points in that one screen).
