confirm the code does what you think it does. i just copied some code and refactored it into a function assuming that it takes me to a particular cell. but actually it was code to assert that this cell is a particular cell. that's why it's important to read code carefully.
another such assumption can be thinking that you read all the code in ana file d you know what it does. it happened to me once, i had read some code a few weeks ago so i didn't bother reading it again and assumed that i have an idea of what it does. turns out i didn't quite understand the code i read the last time and i there were some callbacks i wasn't aware of, which were needed to fix the problem i was working on.
there's no harm in quickly going over what you know once again, maybe
write it in a structured order, start with some questions and read
the code while finding answers to them. ask yourself, do i really understand the code i am working with as that's the most important
question.