> refusing to even acknowledge or entertain criticism

I'm not advocating for you not listen to criticism aimed towards your principle. But if your principle gets put to the test and you abandon it, it's no longer something you fundamentally agree on, it was some "light belief" that you had.

Replace “principle” with “scientific theory.” Why shouldn’t principles be subject to tests and criticism?

If it were due to new facts and information, sure, but a lot of time the "new" principles appear to be self-interest biases manifesting.

Also, if your principles are likely to change quickly, it's probable that they haven't been thought through very thoroughly to begin with. It's not like you have to wait for situations to actually arise to consider them.

In the same way that a scientific theory was meaningless if it failed a test, a principle was meaningless if it needed to be adjusted when actually put to use.

Superseded scientific theories aren’t all “meaningless.” Newton’s laws of motion are superseded, but they aren’t meaningless, and you presumably wouldn’t say that scientists who updated their beliefs in the face of new evidence and explanations were doing anything wrong.

You’re right: “meaningless” was a heavy-handed attempt at continuing the parallel on my part. And sure, they weren’t doing anything wrong, but they fundamentally were wrong in the rules they followed previously. Similarly, if you adjust a principle, you admit that it didn’t hold for you in the first place.

As a tangent: while the parallel to scientific theories is good on the surface, it does lump in this idea that there’s a universal set of correct principles. Isn’t that just philosophy, then? Logical arguments about which principles are sound & universal. Maybe the lesson is to pick principles from the battle-tested ones rather than trying to develop your own.

This is nonsense. Principles should adapt to the context they're applied in. In principle I'm against big government intervention into our personal lives, but you bet your ass I'm in favour of lockdowns when thousands of lives are at stake. I'm not going to let thousands of my compatriots die out of principle.

This is just imprecise statement of principle. It's more like you're against the government intervening unless they're credibly doing it to save lives. If someone discovered how to turn a microwave into a nuclear bomb, presumably you'd support government intervention to collect all the microwaves, even if they had to intervene a lot in our lives. Likewise, you support government intervention to reduce covid deaths, etc.

Sure, you could just say that your “principles” are simply the entire exact sequence of actions you take in your life. That way you could by definition never change or violate your principles.

But usually people use “principle” to refer to a relatively concise statement that can be applied to a large variety of situations.

I'm not familiar with any definition of the word principle that includes the idea of "concise".

Principle as I'm using it here is a moral belief or guide. It's less a description of what you do and more an explanation for why you do what you do.

I just mean that it must be more concise than a lookup table from every possible situational input to the recommended output. The same is implied by the term “explanation.”