Just to mention a few: Not knowing how to use their tools. Now knowing how to read the diagnostic/error messages they received. Not knowing how (and refusing to

Just to mention a few: Not knowing how to use their tools. Now knowing how to read the diagnostic/error messages they received. Not knowing how (and refusing to) to learn new things. Not understanding and/or not caring about the product they were working on, and thus adding bad changes to it. Very frequently one person can bear multiple of these properties. If none of this is familiar to you, then just wait, and you will see how extremely lucky you are...