Wireless peripherals send tiny radio messages every time you move or press a key. If those messages are delayed, duplicated or lost, the cursor stutters or keystrokes appear late. The cause is usually in the radio path, not the device itself.
Distance and obstructions matter. A USB receiver tucked behind a desktop tower, or a Bluetooth device across the room, may not get a clean signal. Moving the receiver to the front of the computer or closer to the device often fixes lag immediately.
Interference from other 2.4 GHz devices is common. Wi-Fi routers, cordless phones, baby monitors and other wireless peripherals all share the same band. A busy environment can drown out the weak signal from a mouse or keyboard.
Low batteries produce a different kind of lag. As voltage drops, the device may skip transmissions to save power, so movements feel jumpy or keypresses are missed even though the device is still connected.