I don't know what's up, but I keep getting the second layer wrong more than half of the time. I'm new and using beginners method, I think. After getting the top layer all white and the first layer simultaneously solved, I look for edges with no yellow in them in the bottom layer. Flip such an edge toward the opposite side of the central color that is identical to the bottom color of the edge. Then do a L or R prime. Then rotate the bottom layer to the left or right respectively, and go like that. Then, get the newly messed up white corner up. The thing is, I keep getting all the bottom edges with yellow in them after repeating the process, and still my second layer is not solved. The idea is once you get all the edges with no yellow in them removed from the bottom, the second layer should be solved. But, in my case, one or more edges are flipped the wrong way. All other colors are solved. I found another similar question, and the thread helped a bit. But I want to know exactly WHY it happens. What am I doing wrong? I've attached pictures for reference. Notice the red-green edge flipped the wrong way.