I partially agree, but it's not about not expecting to reach one's goals...it's about not having any preconceived notions as to how the goal will be reached, or in what way or form. If one doesn't expect to reach their goals or dreams, doesn't think they're within reach, where is the motivation to try and pursue them? Part of setting a goal is deciding whether or not you believe it is attainable for you.
But maybe you'll reach your goal through unorthodox methods. Maybe you'll find what you thought was your goal was only a gateway to something else. Maybe you'll find your dream wasn't what you really wanted. Maybe you'll stop half way and decide you want to pursue something else entirely. To accept these types of outcomes freely, I feel, allows one to let "life" happen.
Instead of an aim-low sort of mentality, I feel one should understand what one feels one deserves and what is within reach, but always be open to new avenues and outcomes.