Transceivers must match the wavelength specifications of the fiber optic cable they are connected to for optimal signal transmission. A mismatch in these specifications can cause significant signal loss or even complete failure in signal transmission, as the light wavelength emitted by the transceiver might not be compatible with the transmission capabilities of the fiber optic cable. This can lead to network connectivity issues. For example, a transceiver designed for 850 nm wavelengths used with single-mode fiber designed for 1310 nm or 1550 nm will not function properly.