1. Nothing is as easy as it looks.
2. Everything takes longer than you think.
3. If there is possibility of several things going wrong, the one that will cause the most damage will be the one to go wrong.

(Other Authors and Sources)

Murphy’s Law: Colrollaries

In Arthur Bloch, Murphy's Law: And Other Reasons Why Things Go gnorW, "Murphyology" (1979). See Murphy's Law.