Without lesson aims you might as well give up and go home, because you suck.
Yet for an embarrassingly long time, I didn’t write any aims for my lesson plans. Sure, I learned all about them on my TEFL course. Yeah, they made sense. But I was busy, and had been told to follow the course book (“two pages of the class book every lesson in class, and one page from the student’s book for homework!”). Surely my aims had just been set for me, for every class?