"Do not think about it too much!"
Translation:Non pensarci troppo!
"Ci" is used in three different ways:
Adverb = there e.g. "Vuoi andare al ristorante? Sì, ci voglio andare." = "Do you want to go to the restaurant? Yes, I want to go there."
Personal pronoun = us e.g. "Ci piace la pizza" = "We like pizza"
Demonstrative pronoun = about/with/in/... it/this/that, or to him/her e.g. "Pensaci" = "Think about it", "Parlaci" = "Talk to him/her"
"ci" is apparently used to replace nouns used with "di", and one or two others. So, if it weren't a pronoun, it'd be "Non pensare di [x] troppo".
Actually in this case is more the "a" preposition: "Non pensare troppo a questo".
The fuller version is that ci replaces a noun or phrase preceded by a, in, su, con, whereas ne replaces things preceded by di, da
Please see my comment at https://www.duolingo.com/comment/4037985/I-began-thinking-about-it-last-year
I understood that "ci", when used like this, means "it" but specifically refers to something in an earlier sentence. "Lo" or "la" can mean "it" but don't necessarily have to refer to an earlier reference. So, when translating from English to Italian without any context, couldn't we use "pensarci", "pensarlo", or "pensarla"?
I completely agree with this. By itself, to say think about it would have to be pensarlo wouldn't it? Lo is the direct object pronoun referring to the thinking? Why MUST it be ci? I get how ci can be translated as "it" as well, but I'm just trying to clarify how pensarlo is marked incorrect