Learn Hardcore Spanish (Latin America): Lo importante es lo que aprendes de tus apuntes, no lo que olvidas. - The important thing is what you learn from your notes, not what you forget.

Spanish often uses lo + adjective to mean “the [adjective] thing/part/aspect” in a general, abstract way. So lo importante = “the important thing.” It’s more natural and concise than la cosa importante here.

Other examples: lo bueno, lo malo, lo necesario, lo más importante.
Note: this lo is neuter; it doesn’t have a plural. You can’t say los importante. To make it plural, you’d say something like las cosas importantes.

All those lo’s—are they the same “lo” as the direct object pronoun (“him/it”)?

No. In this sentence, each lo is the neuter article:

Lo importante = “the important thing”
lo que = “that which/what”
no lo que = “not that which/what”

This neuter lo is different from the masculine direct object pronoun lo (“him/it” in Lo vi). They look the same but function differently.

What exactly does lo que mean, and how is it different from que and qué?

lo que means “that which/what” and introduces a noun-like clause: Lo que aprendes = “what you learn.”
que (no accent) is a relative pronoun/conjunction meaning “that/which/who” with a stated antecedent: La cosa que aprendes.
qué (with accent) is interrogative/exclamatory (“what?”): ¿Qué aprendes? It’s not used here because this isn’t a question.

Could I say lo cual instead of lo que here?

Not in this structure. lo cual refers back to a specific, previously mentioned idea. lo que can introduce a general, unspecified “what/that which.” You could use lo cual like this: Aprendes de tus apuntes, lo cual es importante. But in the original sentence, lo que is the right choice.

Why is it de tus apuntes and not desde or en?

With learning as “learn from [a source],” Spanish uses aprender de:

aprender de tus apuntes = “learn from your notes.”
desde is about origin/starting point in space/time (e.g., desde casa).
en means “in/at.” aprender en tus apuntes doesn’t mean “from your notes.”

You could also say aprender a partir de tus apuntes (“based on/from”), but de is the most natural here.

Do apuntes mean the same as notas in Latin America?

Often, apuntes = “class notes” across the Spanish-speaking world. notas can mean “notes” in some places, but in much of Latin America it commonly means “grades/marks.” To avoid confusion, apuntes is the safer word for “notes.” Collocations: tomar apuntes (“to take notes”), also tomar notas exists but may be ambiguous regionally.

Could I say aprender con tus apuntes?

It’s possible in some contexts, but it usually means “to learn using/with” rather than “to learn from.” For source-of-learning, aprender de is the idiomatic choice: aprender de tus apuntes. You might see aprender con este método/profesor (“learn with this method/teacher”).

Why is it es (from ser) and not está (from estar)?

Ser is used for definitions, inherent characteristics, and general statements. Lo importante es… expresses a general truth. Estar would suggest a temporary state and doesn’t fit: Está importante is incorrect here.

Why indicative aprendes/olvidas and not subjunctive aprendas/olvides?

Indicative (aprendes, olvidas) states general, habitual facts: “what you (typically) learn/forget.”
Subjunctive can appear if the idea is prospective/uncertain: Lo importante es lo que aprendas (what you may/will end up learning). It’s possible, but the indicative is more neutral/general.
With impersonal evaluations plus que, subjunctive is required: Es importante que aprendas de tus apuntes.

What’s the difference between olvidas and se te olvida?

olvidar (transitive): lo que olvidas = “what you forget.” Neutral.
olvidarse with an indirect object: lo que se te olvida = “what slips your mind,” often more accidental/unintentional in feel. Both are correct; the original uses the simpler transitive form.

Should the sentence use sino instead of the comma plus no?

Your sentence is fine: Lo importante es …, no lo que olvidas. It’s a positive statement with a contrasting tag after the comma.

If you want the classic “not A, but B” correction, use sino:

Lo importante no es lo que olvidas, sino lo que aprendes de tus apuntes.

Here use sino, not sino que, because the contrasted element is a noun-like phrase (lo que aprendes), not a standalone clause.

Can I reorder it as Lo que aprendes de tus apuntes es lo importante?

Yes. That’s fully grammatical: Lo que aprendes de tus apuntes es lo importante, no lo que olvidas. Spanish allows that kind of reordering for emphasis.

Why is there no tú? How do I know it’s “you”?

Spanish often drops subject pronouns because the verb ending shows the subject. aprendes/olvidas are 2nd person singular (tú). The possessive tus also signals “your,” matching an implied tú.

How would I make it formal “you” or use “vos” (voseo)?

Formal usted: Lo importante es lo que aprende de sus apuntes, no lo que olvida.
Voseo (e.g., Argentina): Lo importante es lo que aprendés de tus apuntes, no lo que olvidás.

Why are apuntes plural? Could it be singular apunte?

People usually refer to class notes as a set, hence plural apuntes. Singular un apunte is “a note” (one entry/remark). You could say de tu apunte if you really mean a single note, but the plural is more natural for the whole notebook/material.

Can I just say Lo importante es lo que aprendes, no lo que olvidas (and drop de tus apuntes)?

Yes. That makes the statement broader (not tied specifically to your notes). Adding de tus apuntes focuses the source of learning.

Any quick pronunciation tips for key bits?

lo que: the “que” sounds like “keh” (the “u” is silent in “que”).
aprendes/apuntes: stress the second syllable: a-PREN-des, a-PUN-tes.
In Latin America, s is always an “s” sound (not “th” as in much of Spain). The d in olvidas can be softer between vowels.