In my opinion, being asked "are you ready?" is very similar to "are you sure?" which insinuates that I may be making a mistake. Of course I'm not ready: why else would I volunteer to do something / anything different / new?
If you only do things you're READY FOR then you'll never know what you're truly CAPABLE OF achieving. To grow, we must stretch beyond our comfort zones - beyond what we think we're ready for. So no, I'm not ready, and that's cool with me.