It should be noted that seven is also the most likely number to appear as the sum of two randomly thrown and statistically unbiased dice.
This is easily seen when you make a table of all the possible outcomes of the experiment, as follows:
1+1=2 2+1=3 3+1=4 4+1=5 5+1=6 6+1=7
1+2=3 2+2=4 3+2=5 4+2=6 5+2=7 6+2=8
1+3=4 2+3=5 3+3=6 4+3=7 5+3=8 6+3=9
1+4=5 2+4=6 3+4=7 4+4=8 5+4=9 6+4=10
1+5=6 2+5=7 3+5=8 4+5=9 5+5=10 6+5=11
1+6=7 2+6=8 3+6=9 4+6=10 5+6=11 6+6=12
As you can see the most common value is the diagonal of sevens. This is because 7 is the median of the set of all possible results.
Im sure theres a much neater mathematical proof of this, but at this hour I'm afraid a flaky exhaustve proof will have to do...