"Fair is foul, and foul is fair" is from Shakespeare's "Macbeth", and spoken by the three witches in the play.
The phrase means that appearances can be deceiving, and things are not always what they seem; what appears good (fair) might be bad (foul), and vice versa. Some interpretations suggest that the phrase means that nothing is truly good or evil, or that nothing is distinguishable from its opposite.
From the play (Act I scene I, a desert place):
[Thunder and lightning. Enter three Witches]
First Witch: When shall we three meet again, in thunder, lightning, or in rain?
Second Witch: When the hurlyburly's done, when the battle's lost and won.
Third Witch: That will be ere the set of sun.
First Witch: Where the place?
Second Witch: Upon the heath.
Third Witch: There to meet with Macbeth.
First Witch: I come, graymalkin!
Second Witch: Paddock calls.
Third Witch: Anon!
ALL: Fair is foul, and foul is fair. Hover through the fog and filthy air.
- Source: https://www.shakespeare-online.com/plays/macbeth_1_1.html
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Thanks "God", "the Ides of March" came and went without any major issues, other than a lunar eclipse which I couldn't see though the thick cloud. 
But one posting in 投壇 yesterday caught my eye (you can click it to see the context/comments):
We are the generation who witnessed the birth of WWW and high-tech ups and downs, but what is happening now is exponential, much much faster the changes we saw before.
When I left work in Cisco, I was not sure that the internet networks supported by the routers we were building were good or bad for humans.
Now I have similar mixed feelings for this 95% AI coding thingy. Yes, it's a good thing that we leverage AI as tools to help us building the modern world, but what are human and human brains going to be in the future?
I felt lucky that I'm standing at this era point: to witness the big wave of AI, but won't live long enough to be severely impacted by it. But how about our children and their children?
"Fair is foul, and foul is fair". And I'd better stop here. 
