The Serbian military proved absolutely impervious to our most ferocious raids. After many weeks of bombing we took out 6 (SIX) Serbian military vehicles. The military frustration proved too great in Kosovo, so we turned to easy, civilian targets within Serbia.
It was one of the great war crimes of the century. We comitted it.
I'm supposing the precision weaponry simply wasn't as well-developed at the time, plus the Serbs got help from Russia and China in the realm of electronic countermeasures (see #13). But one thing's for certain: the Kosovo operation is solid proof that airpower by itself - unaccompanied by real-time ground intelligence - is vastly overrated.
The more I think about it, the more I suspect that the Serbs were targeted in the first place only because they didn't have modern surface-to-air missiles - as some have pointed out it would've been a totally different campaign if they had the S-300. And later on, when NATO started hitting non-essential bridges and other civilian infrastructure, it did so only because the Serbs had no means whatsoever to retaliate, i.e. with ballistic missiles.