Tôi tưởng ngân hàng đã mở khóa thẻ.

Not exactly.

In this sentence, tưởng usually means something like thought / assumed / was under the impression, often with the idea that the belief may be wrong.

So Tôi tưởng... often suggests:

• I thought...
• I was under the impression that...
• and very often: but apparently that wasn’t true

By contrast, nghĩ is a more neutral think.

So:

• Tôi nghĩ ngân hàng đã mở khóa thẻ.
  = I think the bank has unlocked the card.
  This is a neutral opinion or belief.

• Tôi tưởng ngân hàng đã mở khóa thẻ.
  = I thought the bank had unlocked the card.
  This often implies surprise, misunderstanding, or a mistaken assumption.

Đã marks that the action is viewed as completed or already happened.

Here, đã mở khóa means:

• had unlocked
• already unlocked
• has unlocked, depending on context

Vietnamese does not mark tense the same way English does, so words like đã help show time/aspect.

In this sentence, đã tells us the speaker believed the bank’s unlocking action was already completed.

Compare:

• ngân hàng mở khóa thẻ
  the bank unlocks / unlock the card / unlocked the card
  (time depends more on context)

• ngân hàng đã mở khóa thẻ
  the bank already unlocked / had unlocked the card

Literally, it breaks down like this:

• mở = open
• khóa = lock
• mở khóa = unlock
• thẻ = card

So mở khóa thẻ means unlock the card.

This is the natural way to say that a card has been unblocked or reactivated after being locked.

Be careful not to confuse it with:

• mở thẻ = open a card account / get a new card issued, depending on context
• khóa thẻ = lock the card
• mở khóa thẻ = unlock the card

Because Vietnamese often leaves it out.

In English, you often say:

• I thought that the bank had unlocked the card.

In Vietnamese, the equivalent of that is often unnecessary.

So:

• Tôi tưởng ngân hàng đã mở khóa thẻ.

is completely natural.

You could sometimes insert a linker like là or rằng in other kinds of sentences, but here it would usually sound less natural or more formal than just leaving it out.

It has two parts:

1. Tôi tưởng
   = I thought / I assumed

2. ngân hàng đã mở khóa thẻ
   = the bank had already unlocked the card

So the structure is basically:

[subject] + tưởng + [clause]

More specifically:

• Tôi = subject
• tưởng = main verb
• ngân hàng = subject of the embedded clause
• đã mở khóa = verb phrase
• thẻ = object

So Vietnamese is following a very normal Subject–Verb–Object pattern inside the second clause.

By itself, thẻ just means card.

It could refer to many kinds of cards depending on context:

• bank card
• ATM card
• ID card
• membership card
• SIM card in some contexts

In this sentence, because of ngân hàng and mở khóa, learners naturally understand it as a bank card.

If you wanted to be more specific, you could say:

• thẻ ngân hàng = bank card
• thẻ ATM
• thẻ tín dụng = credit card
• thẻ ghi nợ = debit card

But in real Vietnamese, once the context is clear, speakers often just say thẻ.

Yes, it can be omitted in some contexts, but the meaning becomes less explicit.

Compare:

• Tôi tưởng ngân hàng mở khóa thẻ.
• Tôi tưởng ngân hàng đã mở khóa thẻ.

The version with đã makes it clearer that the speaker believed the unlocking had already happened.

Without đã, the sentence may still be understood, but it relies more on context and can feel less precise.

In this sentence, đã is very natural because the speaker is talking about a completed action they believed had already taken place.

Very often, yes, or at least it strongly suggests that.

In real usage, tưởng commonly introduces:

• a mistaken assumption
• a surprise
• a realization that reality is different

For example:

• Tôi tưởng anh không đến.
  = I thought you weren’t coming.
  This strongly suggests that the person did come.

So in your sentence, Tôi tưởng ngân hàng đã mở khóa thẻ often implies:

• the speaker believed the bank had unlocked the card,
• but then found out that maybe it had not.

That implication comes from tưởng itself.

Yes, very often.

Depending on tone and context, tưởng can be understood as:

• I thought
• I assumed
• I was under the impression
• I had thought

I assumed works especially well when the sentence implies the speaker’s belief turned out to be incorrect.

So if the learner already knows the basic meaning, it is useful to remember that tưởng is not just plain think. It often carries a nuance of mistaken expectation.

Because the bank is the one doing the action of unlocking.

In:

• ngân hàng đã mở khóa thẻ

we have:

• ngân hàng = the bank
• mở khóa = unlock
• thẻ = the card

So the meaning is:

• The bank unlocked the card

If thẻ were the subject, the sentence would need a different structure, for example something more like:

• Thẻ đã được ngân hàng mở khóa.
  = The card was unlocked by the bank.

That version is more passive in feel.

It is written as two words, but it functions together as a verb phrase.

• mở = open
• khóa = lock
• mở khóa = unlock

Vietnamese often forms meanings through combinations like this, where two separate written words act together as one unit of meaning.

Other similar examples:

• bắt đầu = begin
• đăng nhập = log in
• tắt máy = turn off the machine/device

So in this sentence, it is best to learn mở khóa as a chunk meaning unlock.

A native speaker would usually hear it as mildly surprised, annoyed, or disappointed, depending on context.

Because of tưởng, the sentence often sounds like:

• I thought the bank had already unlocked the card... with an implied continuation such as:
• but it still doesn’t work
• but apparently they haven’t
• but my payment was still declined

So even though the sentence itself is complete, it often carries an emotional undertone of:

• mistaken expectation
• inconvenience
• confusion

That pragmatic nuance is an important part of how tưởng works in everyday Vietnamese.