Suicide bombers blow themselves up in order to attack people or property. They may attach explosives to their bodies, which permits them to access crowded areas where placing explosives would otherwise be difficult. Other suicide tactics involve using vehicles to create lethal accidents or run into buildings. Suicide bombers in Afghanistan and Iraq have driven trucks with explosives into buildings to attack them; the 9/11 hijackers flew planes into the World Trade Center and the Pentagon.
Suicide attackers know that they will die for their cause, and are therefore considered the most committed of terrorists. However, there is much professional speculation about the motivations and psychological makeup of suicide bombers.