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Inexpensive pedal fell apart after a few months heavy use.
Inexpensive parts often fall apart more quickly, but plastic pedals especially so: pedals are frequently bashed in to the ground leading to high loads that cause the plastic to shatter or tear, where a metal pedal bends. Plastic pedals can be durable with proper materials and design, but cost and weight go up.
Another not-uncommon plastic pedal failure is for the body to distort enough bearings come out of the races.
See also FAIL-129.html.