When participating in trading competitions or platform activities, we often face the hurdle of "trading volume requirements," such as needing to trade 500U to qualify. To save time, most people choose market orders instead of placing limit orders and slowly accumulating.

On the surface, this seems fine, but after actually executing the trades, you find that your account lost 2~3U, while the fee is only 0.1%? That doesn't add up.

Many think it's caused by coin price fluctuations or inexplicable fees, but the real problem often lies elsewhere.

**The price difference in the order book is the true hidden killer.**

Let me give a real example. How big is the difference for the same coin across different trading pairs?

FOGO / USDT trading pair:
- Buy 1: 0.04050
- Sell 1: 0.04051
- Spread: 0.00001

If you buy and sell once at market price, the theoretical cost is approximately: 0.00001 ÷ 0.04050 ≈ 0.00025, or about 2.5 basis points. This cost is close to a quarter of the fee, which is acceptable.

But switching to FOGO / USDC:
- Buy 1: 0.04037
- Sell 1: 0.04069
- Spread: 0.00032

The cost of a round-trip market trade becomes: 0.00032 ÷ 0.04037 ≈ 0.008, or 8 basis points. That's exactly 8 times the fee.

Honestly, **no matter how low the fee is, if the liquidity of the trading pair is poor, the bid-ask spread in the order book can wipe out your profits entirely.** Even if you carefully design your trading strategy to make a little money, this "hidden cost" can eat it all up in one go, and the feeling is hard to describe.

So next time you participate in a trading competition, don't just look at the fee discounts. Make sure to check the coin's liquidity and whether the spread is large. Sometimes choosing the right trading pair can protect your principal better than just hunting for fee discounts.