You are meant to be reserved upto a point, if the guy noticed that you were not particapating in the convo or held back constantly then he would obviously assume you are not right for him.
I was chatting to a girl and met her twice and she was the outgoing type (through a friend) and yet she just stayed in her shell, lasted 6 weeks, what a waste. Tried chatting about everything but she gave answers which simply ended the topic there and then!!
Always be reserved but upto a point and obviously private issues are private so don't go there.
Don't know if the above makes sense but i'm not going over it again.