Why do we need a ULN2803 in driving a relay?

Why do we need a ULN2803 in driving a relay? Correct Answer for increasing the current

We need a ULN2803 for driving a relay because the relay coil requires 10mA or more current to be energized. If microcontroller pins are not able to provide sufficient current to drive relays then we need ULN2803 for driving relays.
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