"We have a remarkably complete picture in many ways - and it could be that we're not accounting for something that's almost three-quarters of the entire universe"

This quote by Saul Perlmutter is referring to the reality that we have a relatively complete understanding of the universe, however there is still a large part of deep space that we do not understand. This unidentified portion of deep space is estimated to be around three-quarters of the entire universe. This implies that in spite of our present understanding of deep space, there is still a large amount of deep space that stays a mystery. This quote is a pointer that although we have a relatively total photo of the universe, there is still much to be found. It is a reminder that there is still much to be checked out which our current understanding of deep space is far from complete.