Getting overtaken is like milk - it comes in two forms. One cold and easy to digest, the other lumpy, sour and makes you choke.
Type 1 is over before it began. Before you know a blur in your peripheral vision resolves into a lycra clad ghost that disappears over the horizon. You barely have time to register a pair of tightly defined calves moving like hairless metronomes before they're gone.
Type 2 is slow. The sound of grinding gears approaches. There is breathing. You may speed up, to discourage a pass, you may slow down to expedite it. It matters not. After what seems like forever, the (slightly) faster cyclist takes their chance and moves ahead, torso twisting violently as they push their plastic pedals, sweat evident on their brow.
They make slow progress on increasing the gap, leaving you to catalogue a million reasons you aren't going fast today.
BONUS TIP: Of course you can remind yourself it's not a race. But you'll gain about as much satisfaction as from tickling yourself.