This use of figurative language can be seen in a few ways.  One would be through the use of personification, assigning human qualities to a non- human entity.  When "fate asks too much" from the character, it assigns the human quality of demanding on a non human thing (fate.)  It is effective because it highlights to a new level the idea of agony placed upon the character.  Knowing that fate is unavoidable, it adds to this burden when fate "asks" something of another that is difficult to bear.  Another example of figurative language here is the employment of an imagery of agony.  In using this line, London is creating the predicament that his character is immersed in brutalizing agony.  Again, recall that when "fate" asks something, it implies that this weight is inevitable, and, by definition, something that one does not want to do, but has no choice.  The idea of "fate" asking someone to do something conjures up the idea that human beings are not in complete control of their own destiny, and are compelled to deal with elements of reality that place them in agonizing and tough positions of life.