The disposition effect is widely viewed as evidence that investors prefer realizing gains to losses. We show that much of this pattern is mechanical: stable trading styles, when combined with cost-basis accounting, can generate disposition-effect-like behavior even without realization motives. Using linked experimental and field data from Alipay and confirming the pattern in a traditional brokerage dataset, we find that the effect is up to nine times stronger for contrarian than momentum investors. This style is persistent across time and contexts, and so is the disposition effect. Although a zero-return discontinuity supports realization preference, this channel explains only about 10% of the overall effect. The disposition effect is therefore a noisy proxy for realization bias.