So, it's a bit more than that. Let's say I've identified someone that I can't figure out what they're doing. They're just going slower than I expect given what I understand of the work. (I was a professional programmer for over 15 years before management, so this is based on the expectations of a former practitioner.)
Now, why is that? The first possibility is that they ran into a string of tickets that were just harder than we expected at the outset, and it's a statistical anomaly. A second possibility is that this person takes the hardest of the tickets, and anyone would struggle. A third possibility is they are taking tickets past their capabilities as a developer and aren't getting the help they need. In this scenario, they're a capable performer, but are need help to get to the next level. Maybe they're junior, or they're a new employee. If they keep taking these tickets, they will grow and their performance will jump. In these cases, you just keep monitoring.
In the middle case, they may have transitioned to a team or project that is a bad fit, and would thrive on another team or an adjustment to what they're asked to work on. They may be a front end specialist that was expected to pick up back end tickets and struggled from the start. Or, they may be in a temporary dip due to personal circumstances.
Then, you have the negative cases. Their work ethic might be insufficient. They may just not be good at their job and may not ever be able to match the performance at the pay grade and seniority they were hired. Or, you may have a good bullshitter on your team and your numbers tell a different story.
The numbers will tell you if this is a temporary dip. The numbers will tell you if their current output is in line with the rest of the team. From there, the hard work starts.
If you don't have those numbers, it starts looking like a lot of status updates and micromanagement.
Note: remember I am condensing the real work into a few paragraphs. Of course I know it's much more nuanced than I am making it here. This is a surface level treatment.
Also note: Most managers end up doing a lot of part time jobs, of which performance management is a relatively small part. If my primary job was performance and task management, that would be a very bad use of resources for the company.
Now, why is that? The first possibility is that they ran into a string of tickets that were just harder than we expected at the outset, and it's a statistical anomaly. A second possibility is that this person takes the hardest of the tickets, and anyone would struggle. A third possibility is they are taking tickets past their capabilities as a developer and aren't getting the help they need. In this scenario, they're a capable performer, but are need help to get to the next level. Maybe they're junior, or they're a new employee. If they keep taking these tickets, they will grow and their performance will jump. In these cases, you just keep monitoring.
In the middle case, they may have transitioned to a team or project that is a bad fit, and would thrive on another team or an adjustment to what they're asked to work on. They may be a front end specialist that was expected to pick up back end tickets and struggled from the start. Or, they may be in a temporary dip due to personal circumstances.
Then, you have the negative cases. Their work ethic might be insufficient. They may just not be good at their job and may not ever be able to match the performance at the pay grade and seniority they were hired. Or, you may have a good bullshitter on your team and your numbers tell a different story.
The numbers will tell you if this is a temporary dip. The numbers will tell you if their current output is in line with the rest of the team. From there, the hard work starts.
If you don't have those numbers, it starts looking like a lot of status updates and micromanagement.