Don't worry; Merryl Strep does not appear anywhere in this post, except in this first sentence here and you don't have to worry about this one because it's going to end now.
Things I learned this week in Hebrew class (I'm not at the computer that has the Hebrew fonts loaded and my cheat-sheet on the keyboard, so just imagine this has actual Hebrew. I'll fill it in later if I remember.):
1. The root samech-fey-koof means, loosely, "to provide".
2. The words deriving from this root have related meanings; such as, "I have enough", or - work at this one a bit - "we will get there on time".
3. The same root - or at least the same letters, it's not entirely clear - makes the word safek, which means "doubt".
I'm a little surprised I never learned this before; it seems the type of apparent contradiction that rabbis live for. It's possible I did hear and wasn't listening, or forgot. Regardless, we played with this duality for a while in class.
Our teacher suggested it means that when you are content, it creates doubts that you will continue to be content. A variation on the idea that the more you have, the more you have to lose. Or possibly looking forward to say, "Today I have enough; will I tomorrow?" I pointed out a more scholarly bent; to whit, have you ever heard a Jewish scholar be happy when s/he lacked for a doubt? Certainty teaches us nothing; it is doubt that teaches us by driving us to answer it. A bit too much "the rose and the thorn"? Maybe. But likewise it is that fear of scarcity, that doubt, which drives us to achieve contentment; the two concepts are very linked.
There was another idea I liked better, though. To me the connection is a bit of an ironic one. I could easily see it emerging as a joking piece of slang. Or perhaps the irony is a bit deeper than that; perhaps it began as a prayer. When we express a doubt we are, in some way, asking for contentment. We are looking for answers, for reassurance, for security.
This idea exists elsewhere in Jewish teaching; I recall a midrash that tells us when we complain, God says, "You think that's bad? Check this out!" Likewise, when we talk about how good life is, God says, "You think that's good? Check this out!"
Safek could work the same way; an inverse dayenu, if you will. "God," we say, "I am content. I have all the food, shelter, love, and answers that I could ever need." God replies, "Oh yeah? You think so, do you? I bet I can make you even more satisfied with your life!"
Our doubts are our prayers. When we express them, we ask a question. Salesmen, good ones at least, love questions; they know that each one is an opportunity to draw you a little closer. Each doubt we raise, each question we ask, draws us closer to God, closer to perfect contentment.