A lot can go wrong between the time you submit a job to your printer and when it comes back to your door.
Some mistakes are unavoidable. Even if your monitor is exactly calibrated and your printer uses best practices for color management, no printing press can accurately produce the millions of colors available on a monitor. Monitors use projected light created by combining Red, Green and Blue projections sources. Printing presses lay Cyan, Magenta, Yellow and Black (K or Key so as not to be confused with blue) on a reflective substrate–generally paper. CMYK has a color gamut of about 20,000 colors. Even presses that uses a six color process can’t produce over 100,000 different colors.
What’s avoidable are the very common mistakes related to layout. Mistakes like forgetting to add a bleed, putting your text too close to the edge or failing to understand how a fold lines up. Mistakes like forgetting that the mechanical tolerance of the cutting and folding processes are about 1/32nd of an inch at best. That means the cut and fold could be a total of 1/16 of an inch off under the best of circumstances.
Do yourself and your printer a favor. Design a piece that looks great even when everything goes wrong.