The main reason for that is reading material that is too advanced for ones current ability. One should find starting material on a level that matches; you can't run before you can walk. It's easy not to realise this though. As time passes and one becomes familiar with the terminology, it starts falling into place and you can then start handling more intense, terminology-laden articles.
Maths is no different. It's a language, just with different symbols, and you have to learn that language before you can understand it to use it. You can't write a letter until you know your alphabet, words and how they string together; it's the same with maths and science.