Learn Hardcore Italian: Mettilo nella borsa e non pensarci più. - Put it in the bag and don’t think about it anymore.

Mettilo is the second-person singular affirmative imperative of mettere (to put), combined with the direct-object pronoun lo (it). The base imperative is metti, and by attaching lo you get mettilo (“put it”).

Why must lo be attached to the verb in affirmative commands?

In Italian affirmative tu imperatives, clitic pronouns are linked to the end of the verb (enclisis). You cannot say lo metti or metti lo; you must say mettilo.

Why do we say non pensarci using the infinitive pensare instead of the tu imperative form pensa?

The negative tu command is formed by placing non before the infinitive, not by using the imperative ending. So “don’t think” is non pensare, and when you add a pronoun, you attach it to the infinitive: non pensarci (“don’t think about it”).

What role does ci play in non pensarci più?

Ci is a clitic pronoun that replaces a + thing (“about it”). Since you pensare a qualcosa, that “about it” becomes ci. So pensarci literally means “to think about it.”

Why is the prepositional phrase nella borsa used instead of in la borsa or nel borsa?

Nella is the contraction of in + la. Because borsa is feminine singular, in + la borsa contracts to nella borsa. You would use nel (in + il) before a masculine singular noun.

What nuance does più add in non pensarci più?

Here più means “anymore” or “any longer,” so non pensarci più literally means “don’t think about it any more.”

How would you express this phrase politely when addressing someone as Lei?

For a formal (Lei) command you use the third-person subjunctive for the negative and the polite imperative for the positive:
Metta lo nella borsa e non ci pensi più.

What’s the difference between the pronouns lo and ci in this sentence?

Lo is the direct-object pronoun meaning “it,” referring to whatever must be put in the bag. Ci is the locative/indirect-object pronoun meaning “about it,” used with pensare a. They have distinct grammatical roles here.

Could you say non pensarlo più instead of non pensarci più, and would it mean the same?

No. Pensarlo takes lo as a direct object (“to think something, to believe it”), which is different. Standard Italian uses pensare a (“to think about something”), so you need ci for “about it.” Hence non pensarci più is correct for “don’t think about it any more.”