I agree to you, counting those mistakes will help you to be a good trader but that's part of being used to the market. As you become used to the market, you're gaining experience and that's included on it.
Open order is executed due to volatility as soon as the market is open to understand the trading market in advance. An experienced trader can go to profit by making perfect judgment at this time. But apprentices are advised that the first 15-20 minutes of the market start, the time between market hours is less volatile to understand the nature of market movement and the volatility is seen to be revived as the last hour approaches.