I've been intraday trading stock index future for 4 months on a full-time basis. I've noticed that my performance in the afternoon session is significantly worse than the morning session. I'm very curious to figure out what's behind this huge discrepancy. Is this due to myself or due to the nature of the market? I'm a little more tired and less focused in the afternoon, which may contribute to the worse performance in the afternoon to some extent. Is the market more difficulty in the afternoon than in the morning? If so, why is that? I'm wondering whether some other traders face the same problem. If so, how to overcome the problem? Any comments and suggestions are appreciated. Thanks.