10. It's Isaac Newton's birthday.
9. I couldn't decide whether i is the square root of -1 or i are the square root of -1.
8. I accidently divided by 0 and my paper burst into flames.
7. It's stuck inside a Klein bottle.
6. I could only get arbitrarily close to my textbook.
5. I had too much π and got sick.
4. Someone already published it, so I didn't bother to write it up.
3. A four-dimensional dog ate it.
2. I have a solar calculator and it was cloudy.
1. There wasn't enough room to write it in the margin.
Attribution unknown. Photo by dullhunk.