What Arbitrage Is
Arbitrage means buying an asset on one venue and selling it on another where the price is higher, both at the same moment. In crypto that comes down to the same trading pair sitting at two different prices on two exchanges.
A speculator has to be right about where the market goes next. Arbitrage never asks that question. The profit is the gap between two prices at the same instant, which is what makes the strategy market neutral.
Why Spreads Exist
Every exchange runs its own order book, with its own buyers and sellers, and nothing forces those books to agree. That is why the same token sits at slightly different prices from one venue to the next. Regional demand pulls on it, so do deposit and withdrawal fees, and every exchange draws a different crowd of traders.
Most spreads are small, roughly 0.01% to 0.5%, and they don't stay open long. They show up when the market moves hard, when news lands, or when liquidity drains from one venue into another. Catching them again and again takes speed and precision.
Why You Can't Do This By Hand
A spread can close in milliseconds, and no one watches every supported exchange at once. By the time you spot one and get both orders in, it has already closed.
Arbitron does that part for you. It reads market data from every exchange as it arrives, recomputes the spread on each update, and sends both legs at the same time. That is the only way to get filled on something that lasts a fraction of a second.