Learn Hardcore Russian: Я случайно забыл билеты дома. - I accidentally forgot the tickets at home.

Билеты is the accusative plural of an inanimate noun. It’s the direct object of забыл, so it takes the accusative. For inanimate nouns, accusative plural looks the same as nominative plural. (If it were animate, the accusative plural would match the genitive plural.)

What is дома, and why is there no preposition like в?

Дома is an adverb meaning “at home.” It doesn’t take a preposition. Compare:

дома = at home (adverb)
в доме = in the house (inside some house; may not be your own)
у себя дома = at one’s own place (explicitly “at my/your own home”)

Can I say домой here?

No. Домой means “to (go) home,” indicating direction. Here you need a location (“at home”), so you use дома. Examples:

Я иду домой. = I’m going home.
Я дома. = I’m at home.

Where should случайно go? Are other word orders okay?

The neutral, most natural placement is before the verb or at the very start:

Я случайно забыл билеты дома. (neutral)
Случайно я забыл билеты дома. (emphasizes the accident)

Both object-before- or after-дома are common:

Я забыл билеты дома.
Я забыл дома билеты.

Putting случайно at the very end (…случайно) is possible in speech but is less idiomatic here than placing it before the verb.

Is случайно necessary? Isn’t forgetting already accidental?

It’s optional. Забыл already implies a mistake, but случайно adds a clear “by accident/unintentionally” nuance (often softening blame). Near-synonyms:

нечаянно = unintentionally (good for accidents; fine here)
по ошибке = by mistake (often when you chose/used the wrong thing)

Why perfective забыл and not imperfective забывал?

Use perfective (забыл) for a single, completed event. Imperfective забывал is for habitual/repeated actions (“I used to forget tickets”) or an ongoing background process in the past (“I was forgetting…”), which doesn’t fit this one-time mishap.

Can I use оставил instead of забыл?

Yes.

Я случайно оставил билеты дома. = I (accidentally) left the tickets at home (focus on the act of leaving them behind).
Я случайно забыл билеты дома. = I (accidentally) forgot the tickets (focus on the memory lapse). Both are natural in this context.

What’s the difference between дома, в доме, and у себя дома?

дома = at home (usually your own home; default choice here)
в доме = in the house (inside a house; you might specify which house)
у себя дома = at one’s own place (adds emphasis that it’s your own home)

Can I drop я?

Yes, if the context already makes the subject clear. You could say:

Случайно забыл билеты дома. This sounds natural in conversation when it’s obvious who’s speaking. Without context, keeping я is clearer.

Can I replace билеты with a pronoun?

Yes, if “tickets” are already known from context:

Я случайно забыл их дома. Common placements:
Я их случайно забыл дома.
Я случайно их забыл дома.
Я случайно забыл их дома. All are fine; word order changes nuance/emphasis slightly but remains clear.

How do I stress the tricky words?

случа́йно (stress on ча́й)
забы́л / забы́ла / забы́ли
до́ма (“at home,” stress on the first syllable) Don’t confuse до́ма (at home) with дома́ (plural “houses,” stress on the last syllable).

Why no article like “the” before билеты? How do I say “my tickets”?

Russian has no articles. Context supplies “the”/“a.” If you need to specify ownership, use свои (my own):

Я случайно забыл свои билеты дома. Often свои is omitted if it’s obvious the tickets are yours.

Is забыть о билетах a correct alternative?

Different meaning. Забыть о билетах = to forget about the tickets (mentally stop thinking about them). To say you left them at home due to forgetting, use:

забыть билеты дома or оставить билеты дома.

How would I apologize politely using this sentence?

Извините, я случайно забыл билеты дома.
Простите, я случайно забыл билеты дома.

What if I had only one ticket?

Use the singular:

Я случайно забыл билет дома. (male)
Я случайно забыла билет дома. (female)

Is there a concise alternative Russians also use?

Yes:

Билеты остались дома. (The tickets stayed at home.)
Билеты я дома забыл. (focus on “tickets”) These are natural, especially when explaining the situation quickly.

What are the parts of speech here?

Я — pronoun (1st person singular)
случайно — adverb (manner)
забыл — past-tense perfective verb (masculine)
билеты — noun, accusative plural (inanimate direct object)
дома — adverb (place: “at home”)