One of the most detrimental things for a developer is having a team who doesn't understand the developer and doesn't fit the developer's personality. This is often overlooked.

Management likes to try and be 'scientific' and start to micromanage, as if the cause of someone's slowness really is their technical skill. No, it's often psychological in nature. A great manager will have a one on one real talk with you. A bad manager will ask you to log every single thing you do on every single day and instead of caring for you they will immediately delegate the issue away without taking into account the psychological conflicts between employees and hidden bullying. You can't solve people problems with business processes.

What doesn't help: ignoring the issue and just softening it with "It's your first time, you will get used to it" or "You will get better at this over time". No, you won't.

One of the sure ways to let a developer spiral down into failure is to not address these kinds of issues. Don't promote a former employee to manager. I think a real manager has to have the personality and studies for it. People aren't cogs and life is not black and white. You are dealing with people. People are infinitely complex. How often they forget this.