A parachute is carefully folded, or "packed" to ensure that it will open reliably. If a parachute is not packed properly it may result in death since the main parachute might fail to deploy (open and develop) correctly or fully. In the U.S. and many developed countries, emergency and reserve parachutes are packed by "riggers" who must be trained and certified according to legal standards. Sport skydivers are always trained to pack their own primary "main" parachutes. Many skydivers never let anyone else to pack their parachutes because they know the rig is correctly packed when they have done it themselves.