In the first place I worked, bugs were my biggest challenge. The application suffered feature creep and was acutely unstable, such that new errors were discovered on a daily basis and each modification was guaranteed to break something unrelated that would be discovered down the road

The nightmares in the second place were a severely toxic environment coupled with tight deadlines that obviously were always missed. I thought I'd eventually figured out the science of project estimation or feature completion, but it turned out to be more witchcraft than science. I can't possibly have foreknowledge that it'll take me x weeks or days to build this out. And of course, client has to be given a date

I've been back to the job market for a while, unsure even whether I'll still work as a software engineer again. But if I do, I'm also curious about what new major obstacle I'd have to navigate there. It's surprising that development doesn't only have to do with your design patterns, relationships with your code editor, complex functionality you can implement, etc. Other enemies can still do you in