What doesn't make a horse safe to ride

Things I've learned in the past five years:
1.  A short horse

2.  An introverted horse 
3.  If the horse seems to like you then they won't hurt you 
4.  Hoping you've done the right stuff before now
5.  Being attracted to a horse and imagining a relationship

6.  Acting as if the horse read the same books or watched the same videos as you

6a. Buying another book or video 

7.  Using the same techniques as someone else did with another horse

8.  Buying different tack