[kchoudhu]

I just said no one day.

It got easier the day after that, and easier still the day after that.

[mixmastamyk]

This is it simply, part of growing up. Although I might clarify, you could say yes until you plate is full, then you say, "sorry, I'm booked until…"

[kchoudhu]

I actually start saying "no" well before my plate is full. Optionality is good, otherwise sometimes you have to say no even though you would very much like to say yes.