but i think generally speaking the length of trading time frame is inversely related to the winning rate, meaning the more frequent one trades, the lower the winning rate should be. therefore the combination of risk-reward ratio and winning rate together should decide a trading strategy's outcome.
Position sizing will definitely affect one's psychology. if the trade size is too big, I will hesitate to take the loss if wrong and I will hope the price comes back; if the trade is too small, I feel that I don't bother to either take profit or loss simply because the "money on the table" is too small. This is exactly the weakness of human nature. Every individual trader has different risk tolerance, I guess the optimal position sizing is "it shouldn't be too small so that it will has little meaning to change our financial status; at the same time the risk shouldn't be too big so that one can't take it at all. In fact the best strategy should be scalable, independent of human emotion.. I myself witnessed the HFT started testing 1 share in the market, after a while they just migrated the whole strategy to 1 million shares trading. The truth is robot does this the best....
For short term trading, If the trade size is significant enough to an individual, he will definitely plan the trade much more carefully, he will mind each cent for the entry price and the exact moment for the entry timing and thus improve the winning rate.
If we can start a trade at the correct timing and place, the rest will become easier...
