In Act 4, Scene 1, Jaques speaks to Rosalind (still disguised as Ganymede) about why he is melancholy. As he described the stages of a person's life in Act 2, Jaques categorizes different kinds of melancholy, concluding that his is not like any of these. Therefore, he claims that his melancholy is somehow unique. Rosalind is skeptical and thinks Jaques is exaggerating, but when Jaques notes that the "contemplation of his travels" puts in in a "most humorous sadness, Rosalind responds:
A traveller! By my faith, you have great reason to be sad. I fear you have sold your own lands to see other men's. Then to have seen much and to have nothing is to have rich eyes and poor hands. (IV.i.19-22)
Whether or not Jaques' melancholy is exaggerated, he does offer a differing perspective, and somewhat of a skeptical balance in an otherwise "most everyone lives happily ever after tale." Jaques does however show a lighter side. In Act 2, Scene 7, he is in good spirits after conversing with Touchstone:
That fools should be so deep -contemplative,
And I did laugh sans intermission
An hour by his dial. (II.vii.31-33)
Citing this, and some hope when Jaques blesses others as he departs to join Duke Frederick, Jaques is not completely cynical.
But, perhaps the reason for Jaques' melancholy, which seems mostly genuine, is his outlook on life, best expressed in the "Seven Ages of Man" speech in Act 2, Scene 7. While "All the world's a stage, / And all the men and women merely players" is an accurate description of life, Jaques, in his melancholy, might be putting a negative spin on this sentiment. If he means that everyone "acts" in certain ways at different stages and situations in their lives, then everyone is being false - by acting. Thus, his melancholy outlook on life is based on this premise that everyone is being fake, simply playing parts that fit the situation. That means that all actions and gestures, even love, could be marked by some degree of deception.