a construction worker carefully steps across a thin wooden board that spans between two steel beams. The plank bends and sways under his weight as he tries to maintain balance. One end of the board starts to slip from its resting position on the beam. The worker's arms extend outward frantically as he realizes the board might give way at any moment. Other workers below point upward with worried expressions and prepare safety equipment. A supervisor shouts warnings while looking up anxiously at the dangerous situation. a position that is not securely held and dependent on uncertain circumstances