Я оставил кошелёк дома, поэтому не смог заплатить наличными.

I left my wallet at home, so I couldn’t pay in cash.

Breakdown of Я оставил кошелёк дома, поэтому не смог заплатить наличными.

• я: I
• дома: at home
• не: not
• оставить: to leave

Questions & Answers about Я оставил кошелёк дома, поэтому не смог заплатить наличными.

Why is it оставил and not оставлял?

Оставил is perfective past (completed, one-time action): I left (and it’s a finished fact now).
Оставлял is imperfective and would usually mean something like I was leaving / I used to leave / I left (habitually or as process), or it can sound like you’re focusing on the process rather than the result. In this context, the result (wallet is not with me) is what matters, so оставил fits best.

Why does the verb end in -л: оставил?

In Russian past tense, many verbs form the past with -л and then add gender/number endings:

• masculine: остави-л (he/I [male] left)
• feminine: остави-ла
• neuter: остави-ло
• plural: остави-ли

Since the speaker is “I” and (grammatically) presented as masculine here, it’s оставил. A female speaker would say Я оставила кошелёк дома…

Can I omit Я here?

Yes. Russian often drops subject pronouns when the verb form already makes the subject clear.
You can say: Оставил кошелёк дома, поэтому не смог…
But keeping Я is also normal—often for clarity or emphasis.

What is дома grammatically? Why not ?