Ask HN: Do you always FULLY understand the code you are working with?

I wonder if other devs have the same problem as me: i am extremely uncomfortable doing work on code i dont FULLY understand and grasp. Mostly this is due to lack of time, something needs to be fixed urgently, something needs to be extended, etc. I can still get my work done, but as i said, i feel not very good about it (simply put: i hate it).

Is this just me or are other devs experiencing the same?