Well, as an older person I can tell you that of course it is possible to be successful without being a nerd or depending solely on luck.
Your academic grades will fade away in importance as the years pass. So don't become depressed if you are having a hard quarter.
My current boss hasn't finish yet his undergraduate degree, and the organization is paying him the way to get it before he becomes 40. He is not really skillful as an administrator either. But somehow he managed to leverage his relationships with higher level officials and he has a great job security that doesn't depend on his undergrad success neither in his actual performance. Of course I wouldn't say he is successful, but it's just an example.
In the corporation world, there are some basic skills that determine your success:
- Proficiency in your field. Your undergrad grades will play hard here only for the first year. But I've also seen may mediocre students become excellent professionals in their fields after some experience (thanks to motivation, continued training, etc). Your supervisors will really discover your potential not because of your grades, but because of how you perform on the job.
- Perseverance, commitment, hard work.
- Political skills. As mentioned in the previous example, far too many people go up because they purposely manage their relationships with their supervisors. I know when you are young you don't like it, but at least you shouldn't damage your own chances. You should know at least when to keep your mouth shut, if you can't say the right words at the right time. Interestingly though, I remember that in undergrad some students improved their grades or prevented some bad grades using similar techniques with the teachers.
Well, just a short list that I can think of now. Of course there are many more factors, such as specific opportunities, but those lack and are not equal to everyone.
In short, my message is: don't over think it, enjoy your undergrad, try to do better but don't become depressed about your current bad performance.