Software development is filled with fractals. To do A, you break it down into A1, A2, and A3. To do A1, you break it down into A1.1 and A1.2. To do A1.1, you break it down into A1.1.1 and A1.1.2.

In even a small project, that means that your moment-to-moment work might be something like "do task A4.1.2.3.5.3.2.1.5.4". Not literally, but conceptually, that's what's happening. Every task involves a bunch of other tasks, which involve a bunch of smaller tasks, ad infinitum.

This is probably similar to your refueling of a nuclear aircraft carrier. Big tasks involve little tasks, which involve smaller tasks. I assume. I've never refueled a nuclear aircraft carrier. But I have developed a lot of software.

Every software project is a working a plan that has never been done before. Because when it is done, the result is software that is infinitely reproducible, so there is no need to do it again. It's as if somebody needed to figure out how to refuel a nuclear aircraft carrier once. And then after that, everybody who wanted to refuel just cut-and-pasted a fully-fueled carrier.

In many ways, writing software is like figuring out that plan. It's not following the plan, it's creating the plan. And somebody who knows how to do A can figure out that involves A1, A2, and A3. And they can probably figure out that A1 involves A1.1 and A1.2. But they can't predict all the way to A2.3.1.5.2.4.2.2.5.1.1.1.5.2. (It's been tried. It didn't go well. Google "Software Crisis.") Too many issues don't appear until you try to solve them for real.

And those little edge tasks way down at the bottom? They might take five minutes. Or they might turn into another nested set of tasks that takes five hours. Just today, I was working with a team trying to solve a simple problem: print the URL of their current web page. This was no problem. The tool we were using to serve web pages told us the current URL. But it only told us the url's path (the part after the domain name). We also needed the scheme ("https:") and the domain name ("news.ycombinator.com") and the port (":80").

And that wasn't something our tool expected us to want [1]. So a five minute task turned into a half-day marathon of reading documentation, trying things, and reading more documentation. It took us half the day to figure out how to do something that should have taken us five minutes, and we had assumed it would only take five minutes when we estimated the larger task two weeks ago.

Coders who know professional estimating techniques approach this problem by using Monte Carlo simulations that provide a probabilistic range of dates. The high-confidence numbers resulting from these simulations are usually way too far in the future to satisfy stakeholders, because the simulations have a long tail. (More can go wrong than can go right.) Professionals have found it's often easier to refuse to provide estimates than to fight over high-confidence estimates or educate stakeholders in interpreting probabilistic date ranges. Not estimating saves lots of time, too.

I hope this long-winded explanation is the help you were looking for.

[1] For the nitpickers in the audience, I'm obviously leaving out a huge amount of detail about how our REST API was actually interacting with its framework. But that's the gist--we were trying to find a clean way to translate our current absolute URL to another absolute URL. Even now, I'm sure we were missing something obvious.