Harboring the suspicion that there was a curse on composers who wrote a ninth symphony (Beethoven and Schubert were two that had died before their tenths were completed), Mahler attempted to sidestep the threat by not calling his ninth symphonic work a symphony at all. (This was his orchestral song cycle The Song of the Earth.) Only then did he feel safe to compose a ninth symphony, because it was 'really' his tenth. Nonetheless, the curse struck again: Mahler died before he could finish No. 10.
Added by Upcoming Robot on November 26, 2010