Friction: as the temperature drops the grease and oil on the bike works less effectively. Rolling resistance is the biggest drag on forward motion. On the positive side pedaling harder keeps the cyclist warm.
Windchill: moving forward on a bike creates its own windchill. Couple that with a headwind and the additional windchill helps exposed flesh freeze quickly. Fortunately pedaling harder keeps the cyclist warm.
Mind over matter: the joy of cycling may be diminished by cold temperatures, one must train the mind to overcome the lure of warm bodies in bed and get out there with the 10 layers and commute to work. Think of the benefits that mental toughness can bring. It will be easier to deal with the self pity as the frozen dead skin peels off your face while pedaling harder to stay warm.
COLD ARM: probably the most vicious of all winter hazards, combating Cold Arm requires special equipment and planning. Remember, no one wants or needs Cold Arm.