Riddle 43

Men often strive my first to gain
By strength or skill, by speed or worth;
It causes deepest woe and pain,
It causes also joy and mirth.

I watched a tennis-player serve,
And through the air the ball whizzed fast,
But took an unexpected curve;
The umpire said it was my last.

With thoughtful eyes and puzzled brow,
It is my whole you ’re reading now.