Why is it best not to try removing a broken key yourself?

Because the easiest thing is to make it worse. With tweezers, a piece of wire or a hairgrip the piece gets pushed further in, and what was a simple extraction becomes a cylinder change.

The most common mistakes:

• Glue. A matchstick is glued to the piece to pull it out. The glue seeps inside and leaves the cylinder useless.
• Putting another key in. It pushes the piece right to the back and can damage the pins.
• Turning with whatever is sticking out. If the key snapped with the lock half turned, you can leave it jammed.

A locksmith’s extractor is made to remove the piece without touching the mechanism. It is explained in broken key extraction.