I tend to prescribe to the idea that best intentions more often than not create bad outcomes.
A good example of this is the attempt to arrange social events with different groups of friends.
Be that a dinner with old school friends and university friends, or work colleagues and rugby friends or frankly any individual group of mates with another set.
More often than not these occasions go badly.
There is no obvious reason for this to be the case, on paper you like these people and so that should mean that they are likely to get on.
However, people are complex and the likelihood, in my experience, is that these people will in fact not only not get on, but with the added lubricant of alcohol, will often actively dislike each other.
And so before you next try to arrange a large social gathering with a collective of your friends, remember that it is not only important to not mix your drinks but also not to mix your drinks and mix your friends.