1. be no longer able to see or focus on sth
can be literal or figurative
To 'lose sight of' something is to fail to concentrate on it or forget about something important because you are focusing on other (usually less important) things. "We can't lose sight of the end goal here." To 'lose sight' of something is also to be unable to see something because your view has been obstructed or something is too far away. "We tried following your car, but we lost sight of you in the fog." You can find this expression used in both social and professional contexts.