Imagine: you deployed a smart contract on Ethereum, and an hour later you discover that the entire contract balance has gone to an attacker's address. The reason is a classic reentrancy attack: an external call before the state is updated. Mistakes like this cost real money, and they are exactly what separates a blockchain specialist from a beginner who has read a couple of articles.
In this article, we'll break down how development in Web3 works, where mechanisms break, and who should go into this field — and who shouldn't.
Why blockchain is not just "another database"
A blockchain is a distributed ledger where every transaction is irreversible. If in a traditional system an administrator can roll back an erroneous transfer, in Ethereum there is no such possibility. A smart contract is a program that executes on all nodes of the network and changes state only when conditions are met. An error in the contract code means loss of funds with no right to recovery.
The key difference between Web3 and Web2 is decentralization and the absence of a trusted intermediary. Here you interact directly with the protocol, and security is ensured by cryptography and economic incentives. This creates new opportunities (DeFi, NFT, DAO), but also new risks.
Breaking down a real task: how an auditor finds a vulnerability
Let's take a simple storage contract (simplified):
function withdraw() public {
uint amount = balances[msg.sender];
(bool success, ) = msg.sender.call{value: amount}("");
require(success);
balances[msg.sender] = 0;
}
At first glance everything is logical: we send the money, then zero out the balance. But if msg.sender is an attacking contract, its fallback function can call withdraw() again before the balance is zeroed. Such a contract will drain the entire contract balance in a single transaction.
What the auditor does:
1. Checks the order of operations (state changes before external calls).
2. Finds all external calls and checks whether they can cause re-entry.
3. Recommends the Checks-Effects-Interactions pattern or the nonReentrant modifier from OpenZeppelin.
What will go wrong if you skip this: loss of all contract funds. For example, in 2016 the attack on The DAO led to the loss of millions of dollars and the split of Ethereum into ETH and ETC.
Where the mechanism breaks: 4 failure scenarios
Even correctly written code can fail when conditions change. Here are typical situations.
1. Gas limits changed
Ethereum is periodically updated (hard forks). After a change in gas costs (for example, EIP-1559), old fee estimates become outdated. If a contract hard-codes gas for a call, the transaction may fail. How to notice: test on a testnet with current parameters. What to do: use dynamic gas calculation.
2. The rule stopped applying (oracles)
DeFi protocols often rely on price oracles (for example, Chainlink). If an oracle transmits an outdated or manipulated price, the contract may perform a liquidation without a real need. How to notice: check how the protocol handles delays and anomalies. What to do: use multiple sources and timeouts.
3. The term expired (upgradability)
Smart contracts are immutable, but some use proxy patterns for upgrades. If the upgrade logic is compromised or the admin loses keys, the protocol may freeze. How to notice: audit the governance mechanism. What to do: decentralized governance (DAO) and time delays.
4. The tool stopped working (outdated frameworks)
Hardhat and Truffle are constantly updated. If you use an old version, some plugins may stop being supported. How to notice: follow releases. What to do: pin versions in package.json and update regularly.
Learning paths: self-taught vs structured
Self-study of blockchain attracts with freedom, but runs into barriers: no feedback, it's hard to verify the correctness of a solution, information is scattered. Practice on testnets gives experience, but without a mentor mistakes may go unnoticed.
Courses provide structure and error analysis. For example, in the Blockchain and Web3 course, attention is paid to contract security and auditing — topics that are difficult to master alone. However, courses require time and discipline.
Trade-off: self-study is cheaper, but longer and riskier; a course is faster and with feedback, but costs money and requires following the program.
Who it's for and who it's not
Suitable for:
- Developers with programming experience (JavaScript, Python) who want to move into Web3.
- Those interested in finance and want to understand DeFi from the inside.
- Those ready to learn from mistakes and devote time to security.
Not suitable for:
- Beginners without programming experience — it will be hard.
- Those looking for quick earnings without deep immersion.
- Those not ready for the fact that code cannot be fixed after deployment.
Conclusion
Blockchain and Web3 is an area where mistakes are costly and knowledge quickly becomes outdated. If you are ready to systematically understand Solidity, auditing, and security, the Blockchain and Web3 course provides a structured path with feedback on your solutions. Start by learning the basics and practicing on testnets — this will help you understand whether this field is for you.
You can start here: Blockchain & Web3.