whether a person can teach himself a new language would depend on the person's ability to research the language. I'm trying to teach myself Japanese, but there are questions that no amount of reading written documents can teach you.
For example: When do you use a certain word? what words should you avoid using? two or more words have a similar meaning. Are they interchangeable? Where in a sentence does a word belong?
Reading and watching television in another language may help, but you will end up several words that you probably shouldn't be using in many situations, ESPECIALLY if you are learning English.
Fortunately, forums like these exist so you're not alone in your endeavor!
Japanese speakers learning English are blessed with a small syllabary, but cursed with a complicated grammar structure, along with learning to use words such as "a" "an" and "the".
English speakers learning Japanese are blessed with a simpler grammatical structure, but are cursed with a very large syllabary.