Why is Siddartha unhappy? Why is his spirit like a "waiting vessel"?

His spirt is like a "waiting vessal" because he still has not reached Nirvana or the separation of the soul from the cycle of life. He still has more to learn and will not be happy until he has learned all he can from the world and reaches Nirvana. His "vessel" is still not full and he cannot set sail, their are still things he does not understand and things that he is confused by. His lifes goal is to reach Nirvana so his "vessel" will be full and he will have the knowledge to "set sail". He will not stop untill he reaches that goal no matter who or what comes in the way.