That is something you believe to be true. And something I believe to not be true. Have you ever managed large teams of developers? I have. For many years. And I was very successful doing it.
However there was no “objective” way for me to manage the teams. Humans are complex. And the interaction of team members even more so. I have never seen an “objective” metric applied to a team that actually worked without unexpected negative consequences and/or without being gamed by smart team members. If you have an example of an objective metric that has actually worked in reality without negative side effects and without being gamed I would like to hear it.
Your real name is subjective (it depends only on what you decide it is)
Your favourite colour is subjective
Whether you like a piece of art, think it's good or think it achieved what was intend€d is subjective
The meaning of a piece of art is objective but not reducible to a metric and maybe not unique.
This assertion that things are objective if and only if simple models based on overly reductive metrics are the only correct tool for thinking about them is incredibly wrong and destructive.
There are actions that lead to the things you want (whether profit, or a project, or a team that feels fulfilled, a sane and safe working environment, etc) being done, and actions that do not. Sometimes which are which are unknown or even unknowable ahead of time or the only known thing is that attempting to instrument humans and treat them as machines will not work. Sometimes they are very particular to the situation. But once your actions have an explicit goal then strategies for achieving that goal are objective.
That’s quite a claim. Can you give me an example of an objective measurement that isn’t a metric?
None of these things can be reliably turned into a metric that you can measure day by day without one or several highly fallible layers of abstraction. Any model complex enough to capture all the nuances such that you can blindly follow its output can just be called a manager.
Not only that, even if your team was successful in the past, that doesn’t mean that doing what worked in the past will also make your team successful in the future. The context is important. And the context is always different when you start the next project. It might be a different customer, a different problem, a different team (people leaving/joining), a different world (politics/laws) etc.
So what you are left with is your experience, your people skills, and your ability to adapt to new situations. I believe that no “objective” tool will help with that. But I would be happy to be wrong.
So let me ask again: if you know an objective way to improve the likelihood of your team being successful then I would love to hear it. It would be great to have such a tool.
Your problem is you're conflating 'subjective' with 'not instrumentable'. Your name is subjective. You can be in an empty white room and choose it and it will always be correct. So is your favourite colour, or whether you think titanic was good. You can't have a subjective opinion and be wrong (although you can make an assertion about one and learn later that you were confused or that your opinion changed)
Once again, the strategy for achieving your goals once they are picked is objective. If you sit in an empty white room and decide the correct strategy for your software business to succeed in your goal of having a product used by a million people is to fire all your experienced employees, hire apprentice chefs, and instruct them to spend all of their time writing poems by hand you're almost definitely wrong.
The post hoc knowledge is proof that it's objective, not proof that it's reducible in its entirety to a simplified metric.
Metrics are a tool for dealing with some objective problems, so are "your experience, your people skills, and your ability to adapt to new situations". Measurements can also include having a conversation or reviewing someone's work but not trying to reduce it to a small set of numbers.
You need to make some measurements to know if you're in touch with reality, but throwing out everything except some tiny subset of measurements that fit in a policy doc or a kpi outline is just as stupid as making decisions from your white room with no feedback.
This is the almost the very definition of subjective.
However, I do take your point about problems that are objective but that are not measurable or solvable by metrics and algorithms. I would add that to my list of problems for which managers will use the metrics tool, even though it won't and can't work and causing frustration for everyone who is relying on them and/or have to collect the metrics data.
The implication is that the manager is the subject if the object is their interaction with the employee. Thus the answer would be fully internal to the manager if it were subjective.
Of course which answer is correct depends on which problem you are solving. By that metric every problem is subjective.
Reality exists. There are objective answers to management problems. There may not be a unique right answer, and which answers are objectively correct depends on the people involved far more than any oversimplified metric, but that does not make them subjective. It's objectively true that in any long term problem with difficult to measure outcomes giving people agency, allowing them to own their work, respecting them, and communicating in whichever way is appropriate to the particular situation is more effective than trying to treat them like a pocket calculator and maximizing some kpi that isn't even related to the output you want.
The term you are searching for is solvable by an algorithm or measurable, which they are objectively not. I'm fond of Goodheart's law as a rule of thumb as well as keeping in mind the maxim that any measurement both has a cost and is an interaction with the system being measured and thus must change it.