Pendle's principal tokens derive their fixed yield from purchasing below redemption value, but selling before maturity can convert a seemingly guaranteed return into a loss. Market prices and transaction fees, rather than the expected payoff, determine outcomes for early sellers of these yield-bearing instruments. The mechanism highlights the risk inherent in treating principal tokens as fixed-income products: while holding to maturity locks in the discount-to-redemption spread, exiting early exposes holders to secondary market volatility and fee drag that may erode or reverse gains.