How I estimate work

Well, it is the truth. It won't be done before it is done. It is understandable that there is a business that needs to function, but the issue here is the question of asking for an estimate like you've already solved the problem, instead of actually sitting down with the engineer to discuss the business problems that need to be solved. That's what engineers are there for: To solve business problems. Estimates are irrelevant as the solution will be designed with the business constraints in mind.

> it's quite doable to break a large project down into a series of sprints

This too comes across like the problem is already solved. You don't need to break problems down into sprints. That is a ridiculous way to operate. This kind of thing only shows up where there is some weird effort to separate engineers from their jobs.

In fact, "sprint" comes from Scrum, which was designed to be a transitionary exercise to get engineers more comfortable with Agile, which is all about removal of managers. It is intended to teach engineers to think and act more like managers so that when you get rid of the managers completely that they don't flounder. If you are doing it as more than a temporary thing, you've entirely missed the point.

I think this is the most important. You can't just HAVE contingency plans, but you need to be clear in who you need to get approval / sign-off on those contingency plans and who you need to notify. As a developer, knowing that you're going to need to drop Feature B to hit your deadline, but being unable to get the right people to approve dropping Feature B is endlessly frustrating and a massive waste of time on any project.

Basically, yup. It takes a few sprints to start to establish a meaningfully reliable sense of velocity, and the estimation accuracy is why planning poker takes a couple of hours of real discussion over feature complexity, rather than just a few minutes of superficial guesses. But the end result is a far more accurate ability to estimate what a team can reliably deliver in a sprint, and is really good at bringing stakeholders down to earth in terms of what can actually realistically be delivered.

> Seems a bit ironic that complexity doesn't measure time but then we are measuring how much complexity can someone deliver on average on a given time.

What's ironic? And no, it's not about "someone", it's about the the team. Different people on the team will be able to deliver different numbers of points depending on their skill, experience, etc. This is a major reason for not using time -- it actively recognizes that different people take different amounts of time, that things like sick days and meetings are taken into account, etc.

> Isn't complexity directly proportional to uncertainty factors

Yes, this is an explicit assumption of the Fibonnaci-style points usually used.

> and therefore inversely proportional to confidence of time to completion?

Yes, which is precisely why stories over a certain size are disallowed (the feature must be broken up into parts), and why sprints are measured in a very small number of weeks -- to avoid the accumulation of too much uncertainty.

I'm not sure if it's the fun category, but at least they are useful and because of that, satisfying to do. In fact when I finish a solid suite of tests or good, clear documentation, I find it very satisfying. I can't say the same for poker/estimation. I've found to be them a complete waste of time in every job I've had and therefore soul sucking.

> you seem to describe where everybody only works on their specific type of task and can't even estimate anybody else's work, then that's a danger situation when they leave or get sick or whatever and nobody else can step in and everyone's blocked because the only person who can do X is gone

you're conflating the ability to estimate accurately with the ability to implement.

Just because I can't estimate a task accurately doesn't mean I can't do it.