Antonio's two friends suggest a variety of reasons for his somber mood. A condition he, himself is at a loss to explain. He tells them at the beginning of the scene:
In sooth, I know not why I am so sad:
It wearies me; you say it wearies you;
But how I caught it, found it, or came by it,
What stuff 'tis made of, whereof it is born,
I am to learn;
And such a want-wit sadness makes of me,
That I have much ado to know myself.
He admits that his sadness is wearisome for both he and his friends but he does not understand why he feels as he does and that he is at sixes and sevens and needs to learn much about himself to understand his melancholy.
Salarino proposes that Antonio might be concerned about his merchandise at sea. Since he is a sea-merchant, he should surely be concerned about the vagaries of the oceans. Salanio adds that if he were in the same situation, he would be constantly anxious about the direction of the wind and that he would be so worried about every possible risk that, indeed, he would be sad as a result.
Salarino then continues in the same vein, stating that he would be apprehensive about every possible weather condition. He would want to know which way the wind blows or if there is a stillness at sea which could hamper a speedy journey. He would want to know whether there are dangerous rocks or shallow waters which might further impede the delivery of his obviously precious cargo. He asks a rhetorical question in which he expresses the idea that it would only be natural that if one is in such a state of bother that one would obviously be sad.
Antonio, however, assures the two gentleman that it is definitely not his ventures at sea which worry him. He mentions that he is very fortunate in this regard since he has not invested his entire fortune in only one ship or one destination, but that he has a number of ships sailing to a variety of ports. He is confident that his ventures will be a success since he has not placed all his eggs in one basket.
Salarino then suggests that Antonio then might be in love but the merchant rejects the idea as nonsense. Salarino then cleverly and cryptically suggests that if Antonio is not in love either, then he must be sad because he is not happy. It is just as easy as it would be to say that he is laughing and jumping with joy because he is not sad. The suggestion is, of course, meaningless and is obviously an attempt to lighten Antonio's mood.
Salarino then alludes to Janus, the two-faced god and suggests that there are some people who have the strange nature of laughing at practically anything, whilst there are others who will remain sour and not even produce as much as a hint of a smile even though Nestor (a character from Greek mythology who was wont to give advice) would have said that there is much to laugh about if a joke had been told.
Antonio's discussion with the two indicates his naive confidence in destiny. He emphatically believes that fortune will smile in his favor. It is this belief that later drives him into freely signing a bond with extremely punitive conditions with the moneylender Shylock, as a favor to his friend and confidante, Bassanio. Central to this agreement is that Antonio will have to forfeit a pound of his flesh to Shylock if he should not meet the terms of the bond. Unfortunately, it later seems that Antonio might have tempted fate too much and things go horribly awry. But that is another story.