If you are playing aggro/high risk then the amount of punish you receive will destroy you in this matchup because Brawler can punish with a lot of options that can lead into low-damage KO's or just rack up plenty of damage.
I am going to guess this is less about your knowledge about the matchup and more about your style of play. If this guess is correct then you have what many consider to be a much more difficult area of skill to develop because it involves changing your psychological patterns, habits, pre-suppositions, and other integral aspects of your psyche that don't just build your Smash skills but are basic blocks of your entire way of mental life.
Are you a rather jump-to-it type of personality in life? Do you like to get started rather than plan things through? Are you more impulsive about things rather than contemplative? Are you easier to engage in contacting people or leading a conversation? Would you say you are more confrontational about what others say/do?
If you are thinking more "yes" to these questions than not, you are probably an aggro play style and you will continually get destroyed by cognitive players who react and punish you when they learn your patterns.
If not, then it'd be best if you linked us to some videos of you playing this matchup so we can see what is going on.
