Teaching can be very demanding. Many people picture a teacher going in, giving an assignment, and all of the kids sit quietly doing their work while the teacher sits at a desk and marks papers. Just doesn't happen that way! Most people have no clue what the job is truly like on a daily basis.
Example: my niece decided that she "could always just teach" since she didn't think she could get into what she really wanted to do. She observed three days at my school, in several different classrooms, and knew by day three that there was no way she could do the job....she changed her major....
Much will depend on what grade level you are wanting to teach. If you are considering English, than likely you would be at a middle or high school age. You will deal with many different personalities....some who want to be there and learn, others who do not, and have no problem letting you and everyone else know it too.
The key is that you need to like working with the age of kids you would train for. Some people adore the little ones....others would pull their hair out if they had to spend each and every day going over step by step how to do something...only to have to repeat it numerous times! Others find great challenge and reward in working with teens....which would be close to torture for someone else.
You may love English....the challenge would be getting your students to love it, or at least put up with it enough to participate in class and not be a disruption.
Many teachers practically eat, drink, and breathe their work. What still needs to be done is often not far from their minds. To do the job well, you have to be truly committed to it...committed to your students, especially the ones who give you a challenge on a daily basis. You will find you can always do more...but you have to find a balance with your personal life to maintain your perspective.
It is exasperating, exhilarating, frustrating, and rewarding all at the same time. You will love it somedays...and be thinking that a nice, quiet office job sounds really good on others.
Is it hard?.....yes, in fact, close to half of all new teachers quit within the first five years....I don't know of any other profession that has a turn over like that, but it is also one of the most rewarding professions you could ever go into.