You work hard, prove yourself beyond capable, and your Captain rewards you with promotion to Sergeant. You perform feats of valour and dedicate yourself to heroic deeds in the name of the Chapter, you become a member of the 1st Company.
You work hard, slaughter some Imperials, and generally have sound leadership. Unfortunately, there's a brawny fucker who nicked a Thunder Hammer as your rival. You lose the Murder Duel and you die unremembered.
You do no work, betray some people, and manipulate your way into being a Champion of Chaos. You steal a suit of Terminator Armour, and wander around doing unspeakable things and get rewarded lavishly by the gods. Unfortunately, your brothers think you're doing a little too well, and as you sleep one of them comes and slits your throat.
Your leg is severed from the knee by a roaring Ork. As it's axe comes down for the killing blow, your Battle Brother plants a bolt shell in it's eye, blowing it's head off and dragging you into cover. There's a fully stocked apothecarium on the Battle-Barge, and you get an augmetic and a piece of MkVII armour to replace the damaged one.
Your leg is severed from the knee by a roaring Ork. Your brothers see you go down and retreat, leaving you to the Orks until they return to loot your corpse. Luckily, you survive and crawl off, swearing revenge. You're taken to the old ex-apothecary who has to use his Gladius because your warband hasn't seen a Narthecium in four centuries. He takes one of your jokes the wrong way and hacks off the other leg before throwing you to a Spawn.
Yeah, I think I'd go Imperial.