Being an Adventurer is dangerous and tiring work. People are constantly trying to kill you often using some ingenious methods to do so and if that wasn’t bad enough, adventurers regularly end up in the most hostile of environments that can frequently finish off the unprepared and unwary. To survive all these threats and come out the other side of a particularly tough expedition with all limbs intact and a grasp on reality is no easy task.
It’s no surprise then that those roving, inquisitive and daring individuals that partake on these precarious ventures for fame and fortune have a hardiness and toughness to them that allows them to soldier on with injuries and illness most people would succumb to. Those with a naturally strong constitution will stand a good chance of surviving and when rolling up a new character constitution is probably one of the most essential attributes to aim to get a bonus in.
The Constitution attribute will normally directly affect the amount of hit points or damage a character can take before succumbing to their injuries and being knocked unconscious or killed. For example, a D&D 1st level human fighter might have a total hit point score of 12 made up of 9 (1d10 roll for class), +3 (constitution attribute of 15 giving a bonus +2 and +1 added to the attribute score for the human attribute).
Whilst that might not sound a lot, if you factor into Armour Class and other things then unless that character is unlucky chances of surviving are pretty good. Compared to the starting hit points of a D&D Wizard, that constitution bonus is mighty handy to those that wish to play an up-front damage dealer.