If only I knew!
Actually, I do know. The problem is putting it into practice.
So I've been tackling some of the conditional tenses. The sentence "Keşke bilseydim!" would be along the lines of "I wish I knew!", but in typical Turkish fashion, things are folded into verbs. Looking at the verb "bilmek", I can absolutely recognize that it's past tense. But the simple past tense would be "bildim", "I knew". That "sey" stuck in the middle is what tells the verb it's an "if/wish" verb.
So my problem currently is putting this into practice. When I read it, I have no trouble understanding it. My problem comes when I try to actually use it myself. English, of course, doesn't fold these concepts into verbs at all, so I struggle, and blurt something like "Eğer bildim" out, which my Skype partner says is understandable and actually a common mistake for non-natives to make. "Eğer" is the literal word "if", and I suppose it's good to know that people will still understand me if I use it that way.
But it's frustrating when you know how something should come out, but in the heat of the moment you produce something else.
The "Keşke" is a reinforcer for 'if only"or "would that", by the way.
Keşke bilseydim, indeed.