The answer really is plain and simple. You cannot ever be one hundred percent sure. I am talking about everything in life from, a girlfriend, to a career choice, or even something as small as what you really want to eat today. Being unsure is totally fine. I saw an article the other day and it really opened my eyes to the term of "lost". It does not necessarily have a negative connotation to me anymore. Thinking now if I was sure about my career when I was a kid I would have never come to school and I would be fighting fires somewhere out in California right now instead of doing what I love.
If I was so sure about being scared of traveling and foreign places I would never have traveled to Europe or be going back next semester. If I was so sure about my views on relationships, I probably would be a very lonely person right about now and not about to celebrate my one year anniversary. I would have never thought that I could make a difference in the lives of kids, or travel to far away countries for half a year, or even be tied down. So, all of these things that I thought would never change have changed and all of them for the better.
Those are just personal examples, but if you think back to a time in your life where you were so sure about something and now that thing just is not you, then you seriously understand. It is OK to be lost, even in your twenties. I almost feel like if you are not lost at twenty then you are kidding yourself. You really do not have to have stuff figured out to be happy at this point, so do not feel like you have to. You should feel like you are happy to be on a journey, not happy that you think you found the generation. I am not saying to stop being content, because contentment is totally fine.
Although, I am saying that blind naivety will lead you into a place of discouragement and unhappiness if you let it. You have to find that balance between letting yourself be happy, and not letting yourself creep into monotony and dullness. Make yourself do things that are uncomfortable and find your footing. Like climbing a hill, it is important to not stand in one place for too long otherwise I guarantee you will fall back down that hill. You have to keep moving slowly, but surely, up that graded pathway of uncertainty to hopefully find happiness at the top. Understand however, that some hills have nice areas to sit and stay and the view might be nice from there. Although, it is important to remember that you can see a lot more from the top and you should not sell yourself short.
In conclusion, you will not ever be one hundred percent sure. You may find happiness early in life, but you may still be lost and that is fine. Find your place of contentment and stay awhile, but do not be afraid to keep moving because the view is a lot better from the top.