This encapsulates it well, please pray for me.
from The Merchant of Venice Act I scene i
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.
And just in case you were curious this is not the explanation:
"Your mind is tossing on the ocean;
There, where your argosies with portly sail,—
Like signiors and rich burghers on the flood,
Or, as it were, the pageants of the sea,—
Do overpeer the petty traffickers. . ."
To use Shakespearean terminology--would that I had argosies to fret over. Or to paraphrase Tevye, "Would it harm some grand eternal plan. . ."
But that's not the cause either.