Which four factors does the CDL manual identify as the causes of a skid?

49 CFR 383.111(a)(15); AAMVA CDL Manual (nhcdm.pdf) Section 2.19, p. 2-36

Most skids are preventable because they trace back to one of these four driver actions rather than bad luck. Knowing the four causes helps a driver recognize, before a skid starts, when they are braking, steering, or accelerating too aggressively for the road conditions.