I was a little upset just because we now had to find someone else...but I ended up finding my current assistant who is AWESOME.
In the end, she is happier being closer to home, my current assistant is happy having a job, and I am happy having a great assistant. So 3 people are happy compared to 2 people maybe being happy or possibly miserable because maybe it wouldnt have been a good fit
She was very professional about it and I have never held it against her and if I ever encounter her out in the world it will never be a source of animosity
Long story short: If you find a better job tell them quickly and be honest...also take timing into account....dont be the one who quits right before summer band....there is a 45 day rule for a reason