Occam's Guillotine

Reality actually exists and has properties you can determine through study and experimentation.

Sure, agreed.

Conclusions follow from their premises and it’s unreasonable to expect a plurality of truths.

Sure agreed.

Our universe is consistent

Yep

your understanding of the pieces should fit together.

Why? This seems like a classic mistake of naive rationalism. Models exist for reasons, and brains have limits. Depending on my use case, It may make sense for me to have a set of heuristics I know don't fit together becasue they're useful.

To use an example from elsewhere in the post, tensile strength is a leaky abstraction compared to something like the universal wave function, but the former is much more useful for building bridges. Meanwhile, a firefighter is going to be using heuristics like "close to breaking" and "how much weight it can bear" or even a vague feeling of "danger" that is only a leaky abstraction of things like tensile strength.

Now, 'should' my understanding of all those pieces fit together? Not really, depends on what I want to use those models for.

Like Cicero, he was doing philosophy at a time when philosophy meant living a better life. He found suggestions farmed from different systems of thought, but which practically helped one live a better life, and helped form a foundation for stoicism, a set of tools and heuristics for living better. "Should" he have created a set of principles that were completely logically consistent? Well, it may have helped him generate more. But, in terms of a set of practical tools and thoughts that helped one live better, he did quite well curating using an eclectic style.

I think there are two issues here: 1) what are the right beliefs to have about life 2) what's the right emotional attitude to life. You paint a picture of truth as a harsh destroyer of illusions, but why not describe it as a source of wonder / beauty / power / progress instead?

For example, I recently saw a discussion of necessity on a ‘rationalist’ forum where someone pointed out that it was impossible to fly unassisted.

If you don't consider a device like a bike assistance, I think it is possible.

"You can’t design a bridge without actually knowing the tensile strength of steel and the compressive strength of concrete, these facts are not open to interpretation. Designing a society is no different [..]"

Distinguish necessity and sufficiency. There may be some objective truths that can be leveraged for social engineering, but it's obvious that designing a society also involves solving questions outside the hard sciences, going from social psychology to ethics. You're begging an enormous question there.

There's Occam's Guillotine and then there's Ockham's Guillotine. The latter is directly relevant to algorithmic information theory's truth claims and, if funded to the tune of the billions it should be, will terminate the quasi-religious squabbling over social policy that threatens to turn into another Thirty Years War in the not-too-distant future.