One should not be elated on having his desires fulfilled or disappointed in them being frustrated. To be elated in the fulfillment of desire is deceptive, for gain will certainly be lost ultimately.
Therefore, elation must end in pain at some future date. One should not give way to feelings of pleasure or pain, come what may. How do events affect a person? You do not grow by acquiring something nor wither away by losing it. You remain what you always are.