Ways to Go Wrong Tally Sheet
Didn't read the question properly.                                
Didn't copy down the details correctly.                                
Typo in the question/paper.                                
Work for ages and prove 0=0.                                
Get stuck for ages when reading because you don't see why something is true when it is explained in the next paragraph.                                
Work for ages then find a 1 line proof that the entire method is doomed to fail.                                
Work for ages, then find a trivial proof.                                
Prove something trivial via a long and complicated method.                                
Tried to prove something you didn't need to.                                
Tried to prove something false.                                
Your technique works so well that it proves false things.                                
Assume something false.                                
Assume something equivalent to the result.                                
Use a theorem without checking the hypotheses apply.                                
Forget to deal with all of the cases.                                
Convince yourself your proof is correct when it is false.                                
Invent your own notation, which screws you up.                                
Prove math inconsistent.                                
Prove yourself inconsistent.                                
Forget to drink your coffee.                                
Getting distracted.                                
Getting bored.