Brenda,
That is annoying!  What I try to remember to do is to ask in the format of "Don't spend time on this but do you know off the top of your head?"

But recently, I asked someone a question I'd already spent a lot of time researching and it appears that I couldn't do what I wanted to do.  

But, as I said, if I think something should be possible, I won't let a 'No' remain so and will ask again every few months.  Even if it's a 'No' now, things change quickly.  

Anyway, I forgot to add 'off the top of your head' and I'm afraid 1-2 hours might have been spent searching for me to return the first bit of text my researching revealed.  

I feel so bad about that slip of the tongue.