How do YOU know you're gay?

When I came out to my sister, she asked me, "How do you know?" I was a bit flustered for an answer and said, "I just do," but later after thinking about it more, I explained that I know who I'm attracted to like she knows who she's attracted. For her, it made sense and that was that.

Not so for my mother. She keeps asking me how I know, how I'm certain that I'm certain that I know. I've tried to explain this in ways she'll understand, even going so far as to compare my being gay to her conversion to Judaism: Just as she always felt Jewish in her heart, I've always been gay in mine. But still, she can't seem to grasp how certain I am--and not being able to articulate my certainty in plain words does no help to assure her that I know who I am and who I'm attracted to.

So how do you know you're gay? How do you take this deeply personal part of your being and put it into words so diluted of personal significance that others can understand them?