What is DeFi? A careful introduction

DeFi is genuinely interesting technology and genuinely not a beginner destination. If you are not yet completely comfortable with wallets, seed phrases and transaction approvals, this material will cost you money. Come back after the Wallets & Security path.

What it actually is

DeFi rebuilds financial services as smart contracts instead of companies. You connect a self-custody wallet and interact directly: lend assets and earn a rate, borrow against collateral, swap tokens, or supply liquidity to a market.

There is no application form, no approval, no minimum balance, no geographic restriction and no account. The contract treats every address identically. That is the genuine innovation — permissionless access to financial primitives.

What it is built from

• Lending protocols. Suppliers deposit assets into a pool; borrowers take from it against over-collateralised positions. Rates adjust algorithmically with utilisation.
• Decentralised exchanges. Automated market makers price swaps from the ratio of assets in a pool rather than an order book. See DEX.
• Stablecoins. Both the collateral and the unit of account for much of the ecosystem.
• Derivatives and yield products layered on top of all of the above.

These compose — one protocol’s output becomes another’s input. Composability is powerful and is also why a failure in one place can cascade through several protocols that depended on it.

The four risks with no traditional equivalent

1. Smart contract risk

The code is the whole system, and code has bugs. Hundreds of millions of dollars have been drained through contract vulnerabilities, and because transactions are irreversible, the funds are simply gone. An attacker exploiting a flaw is doing exactly what the code permits.

Audits help but do not settle it. Plenty of audited protocols have been exploited. An audit is a point-in-time review by fallible people, not a proof of correctness — treat “audited” as one weak positive signal, not as safety.

2. Liquidation risk

DeFi borrowing is over-collateralised: deposit £150 of ETH to borrow £100. If your collateral falls in value past a threshold, the position is liquidated automatically and you lose the collateral plus a penalty. There is no margin call, no phone conversation and no discretion. In a sharp fall this happens within minutes, and network congestion during exactly those moments can prevent you adding collateral in time.

3. No recourse

No support desk. No reversals. No compensation scheme. No regulator to complain to. If you send to the wrong contract, approve something malicious, or a protocol fails, that is the end of the matter.

4. Governance and admin keys

Many “decentralised” protocols have admin keys or upgradeable contracts, meaning a small group can change the rules, pause the system or in some cases move funds. Governance tokens are often concentrated enough that a handful of holders decide outcomes. Before using a protocol, find out who can change it. The answer is frequently “a multisig of five people”.

Where the yields come from

Sustainable DeFi yield comes from fees users actually pay — borrowers paying interest, traders paying swap fees. That is real and usually modest.

Anything substantially above that is typically token emissions, which is dilution rather than income, or it is compensating you for a risk you have not identified. A yield far above the rest of the market is not an inefficiency you found first.

Practical safety

• Use a separate wallet for DeFi, holding only what you are prepared to lose. Never connect the wallet holding your long-term savings.
• Read every approval. An unlimited token allowance to an unknown contract can empty your wallet later.
• Periodically review and revoke old approvals.
• Prefer protocols with long operating histories, large value at stake and no exploit record. Time is the only real test.
• Start with an amount small enough that losing it teaches you something rather than hurting you.

What to read next

Next: yield farming and the truth about APY.