Learn Italian: Aveva detto una bugia, ma non era mica stupido. - He had told a lie, but he wasn't stupid at all.

Yes, you could just say non era stupido (he wasn't stupid), but mica adds a strong emphasis. It translates to "at all" or "in the least." In this context, mica also carries a subtle undertone of "contrary to what you might expect." Because he lied, you might think he was foolish, but the speaker is pushing back against that assumption.

Why is mica placed after the verb era instead of before it?

When you use non to make a sentence negative, mica acts like an adverb and usually goes right after the verb (or the auxiliary verb in compound tenses). The standard formula is non + verb + mica. This is the exact same pattern you use with other negative words like mai (never) or più (anymore).

Can I use mica without non in this sentence?

Yes! In spoken Italian, you can completely drop the non as long as you move mica to the front of the verb. You could say ...ma mica era stupido. The meaning remains exactly the same, though it sounds a bit more conversational and colloquial.

Why does the sentence use aveva detto (had told) and then switch to era (was)?