How does a garage door come off its track?

A garage door comes off its track when rollers that guide door along vertical and horizontal tracks slip out of tracks due to mechanical failure, impact, or wear that causes misalignment. The most common way is impact from car, as even low speed bump can bend vertical tracks inward or outward, causing gap that allows rollers to pop out, leaving door crooked and jammed. Broken torsion or extension springs cause loss of tension that keeps cables taut; when spring breaks, cables go slack and one side of door drops, pulling rollers out of track. Broken or frayed cables that snap or come off drums cause uneven lifting, with one side falling and rollers derailing. Worn, cracked, or rusted rollers that have lost ball bearings bind in tracks and can jump out when door is operated. Loose or missing bolts that secure vertical tracks to wall allow tracks to spread apart, creating gap for rollers to fall out. Operating door manually too quickly or unevenly after pulling emergency release cord can cause cable slack and rollers to leave track. Closing door on obstruction like trash can or toy pushes bottom out and forces rollers out. Tracks themselves can be bent from improper installation where vertical tracks not plumb. Lack of maintenance like not lubricating rollers and not cleaning tracks contributes. To prevent, avoid hitting door, maintain springs, keep tracks clean and tight, and have annual professional inspection.