Mabil, the only Australian in the Spanish top-flight, enters the World Cup in Qatar with limited recent game time.
In the past two months, Mabil featured just four times for Cadiz - and he doesn't know why.
"The coach ... hasn't really given me a reason," Mabil told reporters in Doha on Friday.
"I couldn't dwell. I just had to look forward to the future. And the future was the World Cup.
"For me, I had to be in the best shape that I possibly can and do what I can control and that was my extra trainings when I don't play.
"It was very frustrating because I know I can make an impact.
"For me, it didn't really make sense why all of a sudden I didn't come on for especially two or three games in a row, that was strange."
The 27-year-old said he had to turn the negative into a positive.
"It brings a new challenge, for me to develop my mind and how I deal with these kind of challenges is something that I had to learn," Mabil said ahead of Australia's World Cup opener against France next Tuesday (Wednesday AEST).
"I didn't take it well at the start.
"But now ... I find a way to get the best out of my days every single day and that is what I can control and be happy with that."
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