Fail what? The only checkride I ever failed was my first initial CFI ride and that was because my instructor who had been teaching for 10 years still didn't know how to teach. Or more explicitly he didn't know how to teach people to teach. He didn't know the difference between a single and a multi engine prop governor and the only diagram he had was a multi engine governor. He taught me that and because I was never taught correctly when I got my multi I didn't know the difference. I failed on systems while explaining a multi engine prop governor as a single. As you know they work in reverse.
there are good instructors and bad ones. If he did not teach you systems shame on him! You have to do your homework. I advise people before attending airline training is to learn as much in advance as you can. Learning Turbine systems and operating procedures in advance will make it easier in the long run. Its difficult to know what airplane you are going to fly until the first day of class but knowing the generics will go a long away.
Before my next checkride I had lesson planned almost the whole PTS for the CFI. Needless to say I had done my research. I realize I'm responsible for the knowledge but there are far to many sorry CFI's out there. I'm going to do the best I can to be a good teacher.
Define failure. Often failure is nothing more than proving that there is a better way, and eliminating a lesser possibility. In such a case, one man may see a failure, but in truth, it's a success. I believe it was Edison who commented that he had successfully found some 2,000 ways for a light bulb not to work, before developing a working example. He eliminated all the ideas that did not work, and in so doing, created a source of light. Others saw his former attempts as failures, but he saw them as steps to success.
Rather than ask what caused you to fail, ask what is helping you succeed.