The sentence is correct and it can be used in written English. For example, you could use this sentence in a reflective essay, journal entry, or personal narrative about decision-making; "As I looked back on my past decisions, I couldn't help but wish I had a crystal ball that could tell me what the best choices were. Even though hindsight is useful in helping me reflect, I often still cannot fully know the consequences of an action until it has already been taken."
"I wish I had a crystal ball," Mr. Koenigsberg said.
"I wish I had a crystal ball," he replied.
He picked up his groceries, saying, "I wish I had a crystal ball".
I wish I had a crystal ball that would show me what the next 150 years will bring.
"I wish I had a crystal ball to tell me if it was a fad or a trend," Ms. Reardon said.
"I wish I had a crystal ball so I could understand what they're all looking for and where this is going," Mr. Scala said.
I wish I had the crystal ball that said, O.K., this is what we have to say or do so we don't lose the next day".
I wish I had written, for instance, this: "Peering into the crystal ball at Italy's future in 2013, what you see is a single stark fact wrapped in mists as thick and shifting as those of the Venetian lagoon".
"I wish I could tell you that I had a crystal ball, but I didn't," he says.
If only I had a crystal ball!
"Five or six years ago I had a crystal-ball vision.
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Cristina Valenza
Retail Lead Linguist @ Apple Inc.