If you want a fulfilling career in ESL you should be willing to delve into the world of psychology, linguistics, self-directed learning, classroom management, etc. Being a really good ESL teacher requires you to have an exceptional repertoire of skills as well as knowledge across a few domains in order to be able to see patterns, synthesize information and then apply them in the classroom dynamics you will be faced with. Your learners are going to change – from semester to semester and from class to class. No amount of pre-made teaching material is ever going to help you help your learners.
It is only through a very deep understanding of Learner (motivations, barriers, etc) Material (the parts and whole of English as a language) and Context (communicative, higher learning, cultural immersion, migration, exam and testing, business, etc) that you can draw your knowledge of other domains into solving the problem of bringing a non-native speaker of English to Functionality / Proficiency or whatever goal you had set out for them to achieve. On top of a very disciplined and methodical commitment of taking a laboratory approach to everyday classroom teaching you will also have to hone a highly perceptive Intuition to make sense of what is going on.
Everyone can become a successful English language learner – if you can speak your MT you can succeed at an L2 and L3. The caveat is that both internal (learner) and external conditions create obstacles to successful language learning.
Tip : If you can dissolve the barriers and obstacles – you will be able to develop successful proficient speakers/writers. If you can have perfect autonomy in your teaching, as I did, then your success rate in producing proficient speakers will sky-rocket.