My first idea was the imagine you're in love type thing, but I feel too cliche.
Yes, it seems like a cliche! So... how can you express your own truth about it. Forget the speech for a second and just ask yourself what insight you gained while thinking about this recently. What little insight have you gained? It is probably hard to explain, but that is what essays are for.
Think of what your contemplation has amounted to, and brainstorm some sentences that really express that insight. That might make your opening line.
But you need to express that fresh insight in a way people can relate to. Catch their attention with a sentence that raises questions in their mind -- questions about the SINGLE MOST IMPORTANT CONCEPT you are sharing in the speech. Do not tell them what they have already heard. Share your newest insights.