You should be slow with other people's code. I bet that if you work on something solo you'd be much faster and that is because you're intimate with the code, you know what could go wrong, where, etc..
Second, the slowness comes from the fact it takes a lot more time to read and understand code that to write it, let alone trust that it is doing what is doing correctly. If you don't introduce bugs and are very careful you won't have nightmarish surprises. Keep up.
Second, the slowness comes from the fact it takes a lot more time to read and understand code that to write it, let alone trust that it is doing what is doing correctly. If you don't introduce bugs and are very careful you won't have nightmarish surprises. Keep up.