Achievements. They're not just great for real life. They're also great for games if you like to show off your accomplishments to friends and other gamers, particularly for ones that may have been a little bit more difficult to come by. The Stadia team seems to love achievements too as there will be an achievements system that will be added to the platform eventually.
Google has confirmed that Stadia will have an achievement system that is similar to other platforms but that it would not be ready by the time Stadia launches in November, further mentioning that it would be coming a little bit later. Those wondering when Google will add this feature will want to turn their attentions to the upcoming Stadia roadmap, which google plans to release in the future.
This particular roadmap will showcase the features that Google is planning to add to the Stadia service, and with an achievement system having been confirmed this will most certainly have to be on that roadmap. Stadia's Director of Product states that he is a "lifelong gamer and a pathological overachiever" and cites these reasons for making the addition of achievements to the platform a priority for them, even if it is one feature which Google isn't going to be adding in immediately.
Doronichev doesn't give much detail on how the achievement system will work but does note that it will be similar to other systems and platforms, and to be quite honest there isn't too much variance one could have with a feature like this. As to be expected, achievements on Stadia will probably be acquired once players accomplish certain tasks in games. One only needs to look at Steam, Xbox, PlayStation, or even Google Play to imagine what that looks like.
What's not clear is how these achievements will be set up. the Stadia team could come up with all of these achievements on their own, work with the developers for each game that supports them to decide on what to add, or it could simply mark down achievements that are available for those games on other platforms and copy those over. The point is that achievements will be there so you'll have something to hunt for.
And hunt for them you shall if you're a collector, but more than using achievements as a means for bragging rights to your friends, achievements give games replay value, and lots of it if some of those achievements are hard to come by, which means players can spend more time being devoted to each game even if they happen to finish any campaigns early on.
Since the achievements system for Stadia will be similar there is likely to be something that is different about it when compared to other systems, what that is though is just as unclear as when they'll actually arrive. Players can rest assured though that they are coming in the future and will probably be there for all the biggest games, and perhaps all the games on the platform.