Shakespeare's play Romeo and Juliet begins by telling the audience, in the Prologue, that true love will not run smoothly. The Chorus, which is often the voice of Fate, explicitly says that "a pair of star-crossed lovers take their life" because of "misadventured piteous overthrows" (Prologue.6-7). Basically it is saying that because of mistakes and sad losses, the two lovers will not enjoy love running smoothly because they will commit suicide. Also, a warning by the Fates should not be taken lightly; therefore, it can be inferred that Romeo and Juliet's love is written in the stars by the Fates and that means it is true love. But again, because of unfortunate events, love won't run smoothly for them and they won't come out of it alive.
The next reference to love not being smooth, or easy, is by Romeo when he is discussing the subject with Mercutio. Romeo was unable to convince Rosaline to love him in the way he desired, so he is heartbroken. Romeo tells Mercutio that love is a heavy burden, to which Mercutio counters by saying "too great oppression for a tender thing" (I.iv.24). He means that love should be tender and easy-going, not an oppression. Romeo then asks the following:
"Is love a tender thing? It is too rough,
Too rude, too boist'rous, and it pricks like thorn" (I.iv.25-26).
Thus, Romeo is saying that love is not a smooth thing. He's been pricked like a thorn because things didn't work out with Rosaline; so, his experience with love tells him it's hard work. Mercutio tries to encourage Romeo to not give up by saying the following:
"If love be rough with you, be rough with love.
Prick love for pricking, and you beat love down" (I.4.27-28).
Once Romeo meets Juliet, though, all thoughts of Rosaline fly out of his mind. All of a sudden, love seems very easy. Upon their first meeting, Romeo is able to steal kisses from Juliet. Later during the balcony scene, Romeo's views of love have seem to change because he declares that "stony limits cannot hold love out" (II.i.9). Juliet is swept away by Romeo's charms and her own desires during this famous scene. She does try to come to her senses, though, by saying the following:
"Well, do not swear. Although I joy in thee,
I have no joy of this contract tonight.
It is too rash, too unadvised, too sudden,
Too like the lightning which doth cease to be
Ere one can say it lightens" (II.i.158-162).
The above passage implies that love does not, or should not run so smoothly, especially if it is happening too quickly. She's also questioning the stability of the relationship because it is getting too serious and they've just met that night. It isn't enough to stop them from setting up a wedding for the next day, though.
Eventually life throws too much at Romeo and Juliet to bear, such as Romeo killing Tybalt and being banished. When Peter tells Romeo that Juliet is dead, Romeo recognizes Fate's hand in not allowing his love to run smoothly and he says, "Is it e'en so? Then I defy you, stars" (V.i.24). It is at this moment that Romeo decides to take matters into his own hands by planning to kill himself. He must figure that if the only way he will be able to love Juliet is in death, then so be it.