It just implies that we havent been through what others have - you cant say we dont know jack about marriages - love or otherwise. You dont consider having seen plenty of friends and relatives get married and how it turns out as experience?
One degree of knowledge is knowing something as a fact, learning from others’ experience, mind is a beautiful thing, of course if used properly. Another degree of knowledge is personal experience, and that makes you a source of knowledge for the other degree of learners! 
For an illustration, we all know fire burns - some of us have first hand experience and some have learned from others’ experience and available knowledge.