Es el principio de mínima afectación en que confiamos.

Because ser is used to identify or define something, while estar is usually used for states, conditions, or locations.

Here, the sentence is identifying something:

• Es el principio... = It is the principle...

So the idea is this is the principle we trust, not this principle is located somewhere or is in a temporary state.

Here, principio means principle, guiding rule, or basic idea.

It does not mean beginning in this sentence, even though principio can also mean beginning in other contexts.

Examples:

• un principio moral = a moral principle
• al principio = at the beginning

In your sentence, it clearly means principle.

This is a fairly formal expression. It means something like:

• of minimal impact
• of least possible disturbance
• causing the least possible effect

Breaking it down:

• afectación = impact, effect, disturbance, impairment, interference
• mínima = minimal / smallest possible

So el principio de mínima afectación is a formal way of saying the principle of causing the least possible impact.

This kind of phrase is especially common in legal, administrative, environmental, or technical language.

Because mínima agrees with afectación, which is a feminine singular noun.

• la afectación
• therefore: mínima afectación

If the noun were masculine, you would use mínimo:

• el impacto mínimo

So the adjective must match the noun it describes.

Because the verb confiar normally goes with the preposition en when you trust in someone or something.

• confiar en alguien/algo = to trust someone/something

So when that idea becomes a relative clause, the preposition stays:

• el principio en que confiamos

Literally:

• the principle in/which we trust

In natural English, we would usually say:

• the principle we trust or
• the principle in which we trust (more formal)

Because confiar needs en.

You say:

• Confiamos en este principio.

So when este principio becomes the relative element, the en must remain:

• este principio → el principio en que confiamos

Without en, the grammar would be wrong:

• ❌ el principio que confiamos

That would sound incomplete because confiar is not normally used that way.

Yes — and for many learners, en el que confiamos may feel clearer and more familiar.

So these are both possible:

• Es el principio de mínima afectación en que confiamos.
• Es el principio de mínima afectación en el que confiamos.

Difference:

• en que = a bit more formal, compressed, sometimes more written or institutional
• en el que = often clearer and more common in everyday modern Spanish

So if you want a safer version as a learner, en el que confiamos is an excellent choice.

Yes, it exists and is perfectly valid, especially in formal or written Spanish. But in many everyday contexts, speakers often prefer:

• en el que
• en la que
• en los que
• etc.

So in Spain, en que is not wrong at all, but it may sound slightly more formal or stylistically condensed than en el que.

Because Spanish often leaves out subject pronouns when the verb ending already shows who the subject is.

• confiamos = we trust

The ending -amos already tells you the subject is nosotros/nosotras.

So Spanish normally says:

• confiamos

rather than:

• nosotros confiamos

You only add nosotros if you want emphasis, contrast, or clarity.

It sounds quite formal and somewhat technical/institutional.

That is mainly because of:

• principio
• mínima afectación
• en que confiamos

A more everyday wording might be:

• Confiamos en el principio de mínima afectación.
• Es el principio de mínima afectación en el que confiamos.

These versions are a little more straightforward.

So yes, the original sentence is grammatical, but it does not sound especially casual.

In many contexts, yes.

That version is simpler because it avoids the relative clause:

• Confiamos en el principio de mínima afectación. = We trust in / rely on the principle of minimal impact.

Your original sentence puts more emphasis on identifying it:

• Es el principio de mínima afectación en que confiamos. = It is the principle of minimal impact that we trust in.

So the original is fine if you want a slightly more emphatic or formal structure, but the simpler sentence is often more natural in ordinary use.

No, they are different words.

afectación

In this sentence, afectación means something like:

• impact
• disturbance
• impairment
• effect on something

This is often used in legal, planning, administrative, or technical contexts.

afección

This can mean:

• affection
• ailment/medical condition
• attachment depending on context

afecto

This usually means:

• affection
• fondness

So in your sentence, afectación is the formal noun related to afectar in the sense of having an effect on or disturbing something.

The relative clause is:

• en que confiamos

It refers back to:

• el principio de mínima afectación

So the structure is:

• Es el principio de mínima afectación
  • en que confiamos

In other words:

• It is the principle of minimal impact
  • that we trust in

A useful way to see it is to start from the simple sentence:

• Confiamos en el principio de mínima afectación.

Then turn el principio de mínima afectación into the thing being described:

• el principio de mínima afectación en que confiamos

That is exactly how the relative clause is formed.

Not with confiar, because confiar takes en, not de.

So you need:

• en que
• en el que

not:

• ❌ del que

You would only use del que if the verb or expression required de.

For example:

• el tema del que hablamos = the topic we are talking about

But:

• el principio en el que confiamos = the principle we trust in

The preposition depends on the verb.

Yes, slightly. The sentence begins with Es el principio..., which gives it an identifying or emphatic feel.

Compare:

• Confiamos en el principio de mínima afectación.
  More neutral.

• Es el principio de mínima afectación en que confiamos.
  More focused on this is the principle.

So the word order is not strange, but it is more rhetorical and formal than the most basic way of saying it.