The gym that I attend is also a squash club (similar to Racquetball). A few weeks ago they hosted a squash championships and I went down to see the finals. I saw three matches in total.
In the first match, the women's final, one competitor was far superior. Technically more proficient, she naturally won.
In the second match, the 'B' league final, both players were equally skilled, but one 'lost it'. Every time he made a mistake he swore and openly chastised himself. He was defeated by his own mind, and naturally lost.
The third match was fantastic: two highly skilled players, both in control of their own minds. At the end of a very long match it all came down to fitness.
Proper technique, mental toughness and fitness.