I always tell my first year teachers when I evaluate them that they probably won't be doing many things in their classroom the same way in year three as they did in year one. No matter how well you think you were prepared to teach in college, you will learn more in the first three months as an actual classroom teacher, than you did in your entire time as a college student.
Teaching is a difficult profession, but it is also very rewarding. It is also constantly evolving. Education tends to be very trendy. New ideas come and go and the good teachers are the ones who sift through it, find what truly works, and take it and make it their own.
For those of us who have been through our first year, reflect back and think about how different you are now. For those who are going through it now or have yet to go through it, know that this is or will be the greatest professional learning experience of your life. Grow from it, learn from it, and become a better teacher from it.