---

1️⃣ What is Blockchain? (Distributed Ledger)

One-liner:

Blockchain = many people keeping the same ledger together

Example:

• Centralized system (like a bank):

  • Only the bank keeps the record.
  • You transfer money → the bank updates the ledger.

• Blockchain (decentralized):

  • Many computers all over the world keep the same record.
  • Every transaction is recorded by everyone.

👉 No single “boss”
👉 Nobody can arbitrarily change the record

• Block = one page of the ledger
• Chain = pages linked together
• Distributed ledger = the ledger exists in many places

---

2️⃣ Block / Block Height / Confirmations

Block

A block = a batch of confirmed transactions

Think of it as:

• Every 10 minutes (Ethereum is faster)
• Pack some transactions
• Make a new page in the ledger

Block Height

Block height = which page this is

• Block #1 → height 1
• Block #100 → height 100

📌 Higher height = older history

Confirmation

A transaction is “confirmed” by blocks piled after it

Example:

• Your transaction is in block 100

• Next blocks:

  • 101 → 1 confirmation
  • 102 → 2 confirmations
  • 103 → 3 confirmations

👉 More confirmations = harder to reverse

---

3️⃣ Decentralized vs Centralized

Centralized (bank, Alipay)

• One boss controls everything
• Can freeze or reverse transactions

Decentralized (blockchain)

• No boss
• Rules are written in code
• Majority consensus counts

One-liner for interviews:

Centralized = trust an institution
Decentralized = trust the rules + math

---

4️⃣ Gas / Gas Fee / Gas Limit

Gas

Gas = computational cost to run a transaction or smart contract

• Transferring tokens
• Calling a smart contract
• Minting NFTs

Gas Fee

Gas Fee = tip for miners/validators

• More fee → higher chance your transaction gets processed first

Gas Limit

Gas Limit = maximum you’re willing to spend

• Not enough gas → transaction fails but fee still spent
• Protects you from infinite costs

---

5️⃣ Why do transactions need confirmations?

In plain words:

Because blockchain is decentralized, transactions need network validation and consensus.
Only after being included in a block and getting enough confirmations is a transaction truly successful.

Even simpler:

It’s not one server saying “yes”; it’s many nodes all nodding together.

---

6️⃣ Why is it immutable?

Three reasons:

1. Hash link

   • Each block stores the hash of the previous block
   • Changing one transaction breaks the chain

2. Distributed storage

   • Ledger exists on thousands of computers
   • Changing it would need to alter most nodes at the same time

3. Consensus mechanism

   • Nodes that don’t follow rules get ignored

One-liner:

Not impossible to change, but too costly, too hard, and nobody would accept it

---

7️⃣ Interview Favorite:

Q: Why isn’t a transaction immediately successful?

Answer (standard):

Because blockchain is decentralized, a transaction needs to be validated and reach consensus among network nodes.
Only after being included in a block and getting enough confirmations can it be considered successful.

Simpler / casual:

Because it’s not one server deciding; it’s many nodes agreeing together.

---

8️⃣ Quick Cheat Sheet

• Blockchain: many people keeping the ledger together
• Block: a page of transactions
• Block height: which page it is
• Confirmations: how many pages piled on top
• Decentralized: no boss, follow rules
• Gas: cost of computation
• Transaction delay: waiting for everyone to confirm

---

好的，我帮你把刚才那套 钱包概念的大白话讲解 + 面试口语版翻成英语，同时兼顾 技术准确 + 面试好说出口。👇

---

1️⃣ Private Key / Public Key / Address

🔑 Private Key

Your wallet’s master key

• Whoever has it controls the assets
• Must never be exposed

📤 Public Key

Derived from the private key, can be shared publicly

• Others can send funds to it
• Cannot be reversed to get the private key

🏠 Address

Simplified version of the public key / account name

• Like a bank account number
• Used to receive funds and identify the wallet

Interview summary:
Private key = control/permission
Public key = public identity
Address = account

---

2️⃣ Mnemonic Phrase / Seed Phrase

A set of words that acts as a universal backup for the wallet

• Can generate the private key (and then public key & address)
• If leaked → all assets can be controlled
• Advantage: just remember 12/24 words to recover the wallet

Interview-friendly version:
A mnemonic phrase is a backup for your private key. It allows wallet recovery but must be kept secret.

---

3️⃣ Why the Private Key Never Leaves the Wallet

Because if it leaves, security is lost

• Wallet = signing device (not an account)
• Private key only used internally to sign transactions
• Never stored or transmitted externally

Interview phrasing:

The private key never leaves the wallet because the wallet acts as a signing device, and the key is only used locally to generate signatures for secure transactions.

---

4️⃣ What a Wallet Really Is

Wallet = signing device + address manager

• Not a bank account, it does not store funds
• Funds are on-chain; the wallet controls signing authority
• You sign with your wallet → the blockchain recognizes your actions as valid

Interview version:
A wallet is a tool to interact with the blockchain. Assets stay on-chain; the wallet just signs transactions on your behalf.

---

5️⃣ Hot Wallet / Cold Wallet

🔥 Hot Wallet

Wallet is online

• Pros: convenient, instant transactions
• Cons: more vulnerable to hackers

❄️ Cold Wallet

Wallet is offline

• Pros: very secure
• Cons: less convenient, harder for frequent transactions

Interview-friendly answer:
Hot wallets are for daily transactions, cold wallets are for long-term storage or large amounts.

---

🔥 Summary for Interview (One Paragraph)

The private key is the core key of a wallet and never leaves it. Public key and address are public identities used to receive funds. Mnemonic phrase is a backup for the private key and allows wallet recovery. Wallets are signing devices—they don’t store funds, they just sign transactions. Hot wallets are online and convenient for daily use; cold wallets are offline and highly secure, suitable for long-term storage.

---