Learn Hardcore Spanish (Latin America): Necesito confianza para hablar en público.

In Spanish, abstract or uncountable nouns used in a general sense often appear without an article. Here you’re talking about the concept of confidence in general, not a specific confidence, so you drop la. If you wanted to specify “the confidence I got from you,” you could say Necesito la confianza que me diste, but for the general idea, no article is needed.

Could I say Necesito tener confianza para hablar en público instead?

Yes, absolutely. Both Necesito confianza and Necesito tener confianza are correct and mean the same thing. The version with tener simply makes the verb tener (“to have”) explicit, whereas the original expresses directly that you “need confidence.”

Why do we use para hablar instead of por hablar or another preposition?

Para + infinitive indicates purpose or goal (“in order to”). You use para hablar because you’re stating the purpose: “I need confidence in order to speak in public.” If you used por, it would convey a cause or reason, which changes the meaning.

Why is it hablar en público and not hablar al público or hablar ante público?

Hablar en público is an idiomatic, set phrase meaning “to speak publicly” or “public speaking.” No article is needed here.
Hablar al público emphasizes speaking to a particular audience (“to the public”), but it’s less common for the general skill of public speaking.
Hablar ante el público is also correct and a bit more formal—it literally means “to speak before the audience.”

What’s the difference between confianza and seguridad here?

Confianza focuses on trust in yourself or self-assurance when you speak.
Seguridad can mean safety or certainty, and in the context of personal traits you’d often say seguridad en mí mismo(a) (“ security/confidence in myself”). Using confianza is more concise and idiomatic for “confidence.”

Does público need an article or gender/number agreement here?

In hablar en público, público functions adverbially (“in public”), so it stays singular and without article. You’re not describing “the public” as people, but the condition of speaking publicly. If you meant “the public” as an audience, you’d say el público, for example: El orador habló ante el público.