SEO first principles
It's easy to get lost in wild speculations with SEO, but good strategies and tactics are always the results of reasoning from first principles.
Scott Fitzgerald, most famous for writing The Great Gatsby, wrote that a testament to true intelligence is the ability to hold two opposing thoughts in the mind at the same time.
For example, you need to specialize (first) and broaden your skillset (later) for many successful careers. Another example: I know I should seek internal validation but still get happy when my Twitter threads get 1,000 likes.
In SEO, two opposing ideas are true right now: it’s both, simple and complex. The basic building blocks of SEO haven’t changed and yet, it seems like there are more unknown factors than ever. Search is still driven by keywords, backlinks, and UX, but there also seems to be an unknown factor that causes rank dips and spikes.
Another ability humans share and that is strongly connected to holding paradox view is to fill empty space. We’re not good at saying “I don’t know” because humans have egos. Our brains are very good at replacing missing information with theories, speculations, and visions. That makes for a poisonous dirty Martiny.
When we don’t understand something, we’re inclined to start wild speculations. We create myths with no evidence a.k.a. fairy tales. As a result, many SEOs work with beliefs that don’t show any impact when implemented. The antidote is going back to first principles. 
What are first principles?
First principles are the most fundamental truths of a concept. Think about the smallest building stone; the most atomic unit.
When interviewers asked Elon Musk how we were able to revolutionize the cars and space industry, he answered:
Physics teaches you to reason from first principles rather than by analogy. So I said, okay, let’s look at the first principles. What is a rocket made of? Aerospace-grade aluminum alloys, plus some titanium, copper, and carbon fiber. Then I asked, what is the value of those materials on the commodity market? It turned out that the materials cost of a rocket was around two percent of the typical price. 
We often work with assumptions and hold views we learned from other people. That’s not a crime. We cannot reinvest the wheel every time. However, it’s important to know when you reason from fundamental truths or hearsay. To be successful in a field, you need to know first principles inside and build all of your other (secondary) principles on top of them.
The way to identify first principles is to collect all assumptions about a space, idea, or concept, and question them one by one. One way to do that is the 5 whys method. In the end, when all evidence has been collected and all assumptions either proven or disproven, you arrive at first principles.
SEO first principles
In 2018, I published a post about the 10 ranking factors we know to be true, a first attempt at identifying SEO first principles. I looked at patents, blog posts, research papers, and other evidence to arrive at my conclusions. In this article - consider it a sequel - I go beyond ranking factors (bad word) and into universal truths for SEO and search engines.
SEO first principles
Search is driven by queries/keywords
Search engines use backlinks as a fundamental signal to rank results and discover new sites/pages
A page has to meet user-intent to rank for a keyword (set)
Google prefers brands for branded queries
A page cannot rank without being indexed, and it cannot be indexed without being crawled
Google prefers fast, secure, non-spammy results
Single pages can rank for thousands of keywords
Google ranks search results in local language
Title, internal links, alt tags, and content help Google understand what a page is about
Mobile and Desktop search results can differ
How to apply first principles
So, what do you do with that? Consider them the ten commandments, universal laws, or six sigma checklist. Whenever you encounter an issue or scale your SEO strategy, you need to go back to first principles. If you make an observation and define a theory, check whether they’re in violation. If it does, it’s likely wrong. The only exception is if Google/search engines fundamentally changed the way they operate.
Google does solve more problems with machine learning. At some point (maybe already today) no single person on the planet knows all signals the search engine looks at to rank sites. But that shouldn’t be an excuse to make up wild theories. The majority of problems can still be answered by going back to first principles.