A picture is worth a thousand or 200 words. 

A Bureau of Labor and Statistics (BLS) study states that 72% of workers injured in scaffold accidents attributed the accident either to the planking or support giving way, or to the employee slipping or being struck by a falling object. All of these can be controlled by compliance with OSHA standards.

Scaffolding 1926.451  Failure to provide fall protection 1926.451 (g)(1) is the number 1 fined violation by OSHA

Scaffolding accidents are almost always the result of negligence on the part of the improper construction or maintenance. It is estimated that 100,000 of 500,000 injuries that occur on construction sites are scaffold related accidents. OSHA does have strict regulations when it comes to construction sites using scaffolding and building a safe scaffold. But unfortunately sometimes the contractor or even the laborer thinks some of the steps are unnecessary and overlooks them, sometimes paying with their lives for this mistake.

Accidents involving scaffolding mainly involve people falling, incorrect operating procedures, environmental conditions and falling materials caused by equipment failure. The causes of scaffolding accidents include failures at attachment points, parts failure, inadequate fall protection, improper construction or work rules, and changing environmental conditions (high winds, temperature extremes or the presence of toxic gases). Additionally, overloading of scaffolding is a frequent cause of major scaffold failure.