• Maybe I can keep him/her until I can find a replacement.
• This will wreak havoc on my department's morale.
• I already need to hire one more person, this would make two.
• This couldn't happen at a worse time in our 'deliverables' schedule.
• If I lose him/her, it will really make me look bad.
• Now I'll need to redo the entire vacation schedule.
   

What will your boss say in an attempt to keep you?

• I'm shocked - I thought you were as happy with us as we are with you.
• I've been meaning to tell you about the plans (changes) we have coming up for you.
• The Director has you in mind for some exciting new responsibilities.
• We just finished your raise and will put it into effect immediately.
• You're going to work for those guys ?

Reasons not to take the counter-offer

• The company is suspect if you were forced to get an outside offer to generate internal promotion, salary increase or better conditions.
• Having demonstrated your lack of loyalty, you are forever considered a fidelity risk and lose your status as a team player and access to the inner circle.
• Counter-offers are usually only a stall mechanism until they find a replacement.
• Your real reasons for leaving still exist (be it a better commute, greater technology interaction or training, more autonomy, a more stable or growing company). A raise or other promises only make it more tolerable for the short-term.  Besides, was this forced raise just a later raise coming early (and maybe never again).
• Since you had to give notice, will you have to threaten to quit every time you deserve internal promotion, salary increase or better conditions.
• The best companies don't make counter-offers.  They treat employees fairly and equitably and choose to recognize worth accordingly.