Stuck In The Middle

It's difficult being in the middle of a situation. When you know that no matter what you decide, somebody is going to get hurt or offended, or make you feel in the wrong. But there will always be a time where you have to be the bad guy, and make the decision to piss somebody off. 
In my case, the occasion is my 17th birthday party. I could either have it next Friday on Saturday. If I had it on the Friday, one friend would be late because she works until 10pm. If I had it on the Saturday, another friend wouldn't be able to make it because she'll be working until at least 1am. So I chose to hold the party on the Friday night, triggered by the logical thought of preferring somebody turning up late than not at all.
Of course, the consequences were unfavourable, to say the very least.
My good friend who works Fridays is not impressed. She has decided not to come at all because she'll be too tired, which is admittedly annoying or upsetting, or somewhere in between (though nowhere near enough to pick a fight). I feel terrible about it, but it's a decision I had to make. It wasn't as though I prefer the company of the other friend (as her mother so tactfully put it), and it is by no means personal. The fact was, I had to choose between friends, so I let logic make the decision for me. Evidently, logic doesn't agree with everyone. 
But then again, does anything agree with everyone?