First and foremost, they make us feel good. They satisfy a compulsion to be rewarded for our actions. Most of us mull through life looking to get a pat on the head when we do well at something. It might be school, it might be work, it might be a relationship, but whatever it is, we need to feel like there's a reason for doing what we do; a reason that can often be found in the praise we receive. Getting an "Achievement Unlocked" message upon reaching the end of a level is just the carrot on a stick I need to keep me going sometimes.
Beyond the obvious point that achievements and trophies make us feel swell, they also represent your gaming resume; a scrapbook of sorts. Much like looking at photos of your last vacation, viewing a list of achievements or trophies you've earned can serve to remind you of some great times. They're a way to say, "I've been there. I've seen some stuff. I've done great things." Because we have something to show ourselves and others, they're validation that the time we've spent gaming wasn't a waste. Much the opposite in fact. Achievements and trophies allow us to bolster our sense of self-worth.
Besides being a system of rewards, achievements and trophies also supplement leader boards by providing a new way to compete with friends. I remember the first time I got into a friendly competition with someone (a co-worker) through achievements. I noticed that he was playing a lot of Call of Duty: World at War on Veteran difficulty. He'd already beaten a few levels, so I had to intervene. I caught up with him, then came to work the next day to gloat. From there, we'd each rush home after work each day to try to outdo the other, and for a change, work became fun. We'd share strategies, experiences, and frustrations (grenade spamming anyone?); things that really took my experience with the game to the next level. Eventually he got stuck on Vendetta (the fourth level), and I on Blowtorch & Corkscrew (the 12th level), but even if I wasn't able to finish the game, I still won the competition.
Achievements and trophies may seem simple on the surface, but there's more to them than meets the eye. I leave you with these questions: What are some of your favorite achievements or trophies and why? Do you prefer the acheivements system or trophies system and why?