Patrice: The light came on for me while I was reading a sentence that had an indirect object, and I finally understood that in Spanish, an indirect object must be expressed with an indirect object pronoun, which is then clarified with an indirect object phrase if the pronoun could be confused. The example I used while discussing my epiphany with my tutor is as follows:
"Te escribí una carta." She was sitting across from me and we were the only people present so it was clear to whom I had written the letter.
"Le escribí una carta." No one else was present so to whom I wrote the letter is unclear and needs the clarifying noun phrase: "Le escribí una carta a él," (perhaps pointing at the boy at the next table. Or "Le escribí una carta a mi hermano," or "Les escribí una carta a tus padres."
The confusion for me is that in English we use the noun phrase if the recipient of the action is unclear (I wrote a letter to Sara) OR we can use the IOP if the recipient is clear (I wrote you a letter) but we don't use both in the same sentence.
But in Spanish you must use the IOP (me, te, le, nos, os, les) if an indirect object is present in the sentence, and may use the clarifying noun phrase if needed.
I have not yet taken the time to see if the same idea holds true with direct objects, and I hope that if my reasoning is in error I will be corrected.