Do the words lo, la, los, las (objective pronouns) and este, esta, estos, estas, ese, esa, esos, esas (demonstratives) only have to agree with gender when the word is actually used? What if the pronouns/demonstratives only refer to objects whose words are never spoken? I'll give some examples.
On Direct and Indirect Object Pronouns in Spanish, I saw the following example sentence:
No quiero decírtela. I do not want to tell it to you
In this sentence, we don't know to what word 'la' refers since it is never mentioned, so it would make sense (to me) that 'lo' is used instead (since, for example, 'el' is used instead of 'la' when gender is ambiguous or mixed).
Also, when using demonstratives to point to objects, do you have to make sure the demonstrative agrees with that object, even if you never mention the object by name? If you do have to make the demonstrative agree with the gender, what about ambiguous cases when there are multiple words that refer to the object but have a different gender?
For example, if I point at an apple and say "Look at that" in Spanish, but never say the word "manzana" (or any other words that could refer to the apple, such as "objetivo," which is masculine), what demonstrative do I use?
Part of the reason this is a problem with me, is that making gender agree requires mental effort, especially since I associate gender with words, not actual objects.