When we say high lot size, we mean that the volume we are using for our trading is so far above the ground compare to the size of trading account that we possess. When we use high lot size in our trading session, our trade does not have space to work because when you open a trade does not mean that the market would continue immediately to go in your decision. If you place say a buy in market, this those not mean that the bears in the market would not try their luck to push the market to their side, even if the market is a bullish trend. So, when we use a high lot size, when those pull back comes, we might be stop easily even before the market goes to our market. Do not suffocate your trade but give enough ventilation to breath properly.