Why can't a stablecoin have it all?

The stablecoin trilemma describes the fundamental tension between three desirable properties: peg stability (the coin reliably trades at $1.00), capital efficiency (the protocol doesn't require excessive over-collateralization), and decentralization (no single entity can freeze funds or censor users).

Peg Stability

Fiat-backed stablecoins like USDT and USDC achieve the strongest pegs because they offer direct redemption for US dollars. Any time the price drops below $1.00, arbitrageurs can buy the stablecoin cheaply and redeem it for $1.00 worth of assets, pocketing the difference. This creates a hard price floor. The March 2023 USDC depeg to $0.87 was an exceptional event caused by uncertainty about $3.3 billion held at Silicon Valley Bank -- as soon as the FDIC guaranteed all deposits, the peg recovered within hours. USDT has experienced minor wobbles (dropping briefly to $0.97 during Terra/UST collapse panic in May 2022) but has always recovered quickly due to Tether's active redemption window.

Crypto-collateralized stablecoins like DAI maintain their peg through over-collateralization and liquidation mechanisms. If a DAI vault drops below the minimum collateral ratio (typically 150%), keepers liquidate the position to maintain system solvency. The Peg Stability Module (PSM) allows direct swaps between DAI and USDC at a near-1:1 rate, effectively anchoring DAI to USDC's peg. This is effective but introduces centralization risk since a significant portion of DAI's backing flows through USDC.

Capital Efficiency

Capital efficiency measures how much stablecoin can be minted per dollar of collateral deposited. Fiat-backed stablecoins are the most capital efficient: Circle holds $1 of assets for every $1 USDC issued, giving a 1:1 ratio. USDT operates similarly, though Tether's reserve composition has historically included riskier assets like commercial paper (now largely replaced by US Treasury bills).

Crypto-collateralized stablecoins are inherently capital inefficient. To mint 100 DAI, a user must deposit at least $150 worth of ETH (150% collateral ratio). Many users maintain even higher ratios (200-300%) to avoid liquidation during volatile markets. This means billions of dollars in crypto sit locked as collateral, producing less stablecoin than fiat-backed alternatives. GHO inherits this trait from Aave's lending pools, though it offers slightly better capital efficiency because users can still earn interest on their deposited collateral.

FRAX attempted to solve this through its fractional-algorithmic model. In its original design, FRAX required only partial collateral, with the remaining portion backed algorithmically by the FXS governance token. After the UST collapse demonstrated the fragility of algorithmic mechanisms, FRAX v2 pivoted to 100% collateral backing through its Algorithmic Market Operations Controller (AMO), which deploys collateral into yield-generating DeFi strategies. This improves capital efficiency compared to DAI while maintaining full backing.

Decentralization

Decentralization is where fiat-backed stablecoins fail most dramatically. Both Tether and Circle maintain blacklist functions on their smart contracts. Tether has frozen over $1.8 billion across hundreds of addresses as of 2024, often at the request of law enforcement. Circle blacklisted the Tornado Cash smart contract addresses following OFAC sanctions in August 2022, instantly rendering millions of USDC inaccessible. This centralized control means a single entity can effectively confiscate user funds with no on-chain governance or community input.

DAI scores highest on decentralization, though imperfectly. MakerDAO governance is controlled by MKR token holders who vote on risk parameters, collateral types, and stability fees. However, the heavy reliance on USDC as a collateral type (via the PSM) introduces indirect centralization -- if Circle blacklisted MakerDAO's PSM contract, it could destabilize DAI significantly. The Maker community recognized this and has been diversifying into Real World Assets (RWAs) and reducing USDC dependence, a process accelerated by the rebranding to Sky Protocol.

GHO occupies a middle ground. It's governed by Aave DAO, one of the largest DeFi governance communities, but the Facilitator model means approved entities control minting. The initial Facilitators are the Aave protocol itself and entities approved by governance, giving it more decentralization than USDT/USDC but less than a fully permissionless system.

Where each stablecoin lands

USDT and USDC cluster near the Peg Stability / Capital Efficiency edge of the triangle. They offer reliable pegs and 1:1 capital efficiency but sacrifice decentralization through centralized issuers with freeze capabilities. DAI sits closer to the Decentralization vertex but pays the price in capital efficiency (over-collateralization) and has a slightly weaker peg mechanism that depends partly on USDC. FRAX attempts to occupy the center of the triangle through its hybrid approach, achieving reasonable scores in all three dimensions without excelling in any single one. GHO, as the newest entrant, is still finding its equilibrium but trends toward moderate decentralization with improving peg stability as the market matures around it.