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> Can you imagine if the insurance company started arguing with the repair shop, asking them—no—telling them that they would only pay the $18,000 and not the additional $20,000 because that was the original estimate? Does that sound ridiculous to you? It does to me, too.

No, actually, this sounds quite realistic and in many cases even reasonable. Medical insurance does this literally all the time. Insurance companies of many different kinds in general have to do this to prevent fraud and keep costs (and by extension premiums) low.

> There is no fixed path when modernizing a complex legacy system. There is no rulebook to follow.

Of course not. But as an engineer tasked with this kind of project your estimate should reflect some kind of plan for accomplishing the project, where the plan has more concrete and actionable steps that make estimation easier. And if you are good at your job, your estimate should account for known-unknowns (eg this part is contingent on something partially out of our control and may be delayed by X months) and give enough slack to handle inevitable unknown-unknowns without excessive padding. And uncertainty regarding any particular risks or variance in how long somethign takes should be explicitly noted and communicated.

My $0.02:

The unfixable estimate vs deadline problem ultimately boils down to money. A particular project might be worth it if it ties up 10 people for 3 months, but not worth it if it ties up 10 people for 12 months. And relatedly, businesses oftentimes find themselves needing something finished by a certain time to close a sale/keep a customer happy/catch up to a competitor, and the stakeholders on the other end (customers, investors, partners) need some kind of date for their own planning.

Good estimation is really about identifying the probability distribution of the completion date, rather than a single "expected" completion date, and identifying/communicating the related risks. For a big project this itself probably will take a few days to months to complete and communicate. If you do this properly, there should never be any ambiguity as to what is an estimate and what is a deadline. If you don't do this, you are basically assuming that your manager (and their managers and so on) can read your mind and have the exact same understanding as you do regarding how firm the estimate is + what the risks and possibly "actual completion times" are. You're also denying them the opportunity to help you derisk or accelerate the project by eg adding more people to work on it, reach out to some external stakeholders, or communicating the end date to eg investors/customers in a way that reflects risks. You also need to update the people that care about the completion semi regularly to tell them about any new risks or known unknowns for the same reasons.

If you are wildly off with your estimate even after spending the time to breakdown the project with a more actionable plan, identify risks, and come up with ranges/a distribution of outcomes - let's say you blow past your p99 time to completion - you are probably just bad at your job (or trying to operate above your skill level) and it would probably be very reasonable for your manager to hold you to a deadline with the threat of firing you/canceling the project. Yes, the sunk cost fallacy dictates that even projects that run over should probably be completed in many cases (though since overall budget/personnel are usually constrained I think the opportunity cost of doing other things becomes pretty important). But if people can't trust you to estimate properly they probably can't trust you to lead a project or to have estimated the remaining time to finish the project.

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cplat 6 days ago | parent [-]

This is a very good comment and does reflect my experience. As engineers, we're the only people who can estimate something close enough, and it becomes our job to do that while taking into account the risks.

Our bad assumption is in thinking that only the final output matters, regardless of when and where it is delivered. Like saying that it only matters if the train arrives at the station, regardless of when it does.

The problem is anyone depending on us downstream will get impacted. And yes, estimation is tough, requires foresight, and maybe a lot more things, but that's what being a professional means.

	▲	weitendorf 6 days ago \| parent [-]
		Thank you! And yeah, I think a lot of software engineers miss the forest for the trees in assuming that estimates are "only estimates", in what is implicitly assumed by others (who may not have as much context) when eg communicating dates, and in the assumptions they make regarding constraints that may not actually be constrained (eg the ability to add more people to the project or partially release/launch it with reduced scope, with the remainder to be added later). It's like, people forget that a few weeks of one engineer's time costs their employer tens of thousands of dollars, and that multi-quarter/multi-person projects literally are $1mm-$10mm+ endeavors. A lot of less experienced engineers also are just bad at estimating and don't do a good job clarifying blockers/risks/etc when participating in planning poker with a scrum master/manager, who may also not be very good at their jobs. Obviously a lot of what I wrote is overkill for "you said this was only one story point but it actually took you two days!" but I think this environment being most SWE's first/only exposure to estimation causes them to take the opposite lesson than what they should (that estimation is awful/bullshit, it doesn't matter if you blow past it/everybody always blows past it, you will be argued with if you estimate something as too high, you are incentivized to excessively overestimate to keep your workload low / prevent people getting angry). But that's really only a productive mindset to have when the stakes are low. I do think leaders, from executives to managers/tech leads/"scrum masters", should be more in the habit of proving estimates/deadlines for risks and ranges than they are. A lot of the time these things become games of telephone were eg an engineer comes up with a plan with all the risks identified and detailed completion dates, and then their manager converts that into a single date given to the CEO as a reasonable deadline. That said, if you actively communication the current ETA and risks proactively throughout a project you also end up with a convenient paper trial and give people multiple opportunities to correct miscommunication.