There are four stages to a person’s career:In Stage 1 you are enthusiastic about your work, but inexperienced (start of your career). In Stage 2 you are both enthusiastic about your work and have gained experience (top of your career). In Stage 3 you’re tired of your work, but you are also still competent/experienced (maintenance stage). In Stage 4 you are sick of your work, and because you haven’t been motivated to keep up with your profession, you are now, once again, inexperienced relative to the state-of-the-art in your field (end of career).