Horse going sideways - friend's advice

I spoke to a friend today about our "going sideways" problem.  Now this friend is a bit of a mentor.  He is someone who has been out there, owned various horses, competed in horse trials, and lived to tell the tale.

Well, the minute I said the words "nervous" and "going sideways" in the one sentence, he straightened up, looked me straight in the eye, and gently, but wisely, said "I had a horse like that once.  Tried to event him.  I used to finish the dressage test and people would run up to me saying it looked beautiful.  But it felt like sitting on a time bomb.  The horse would get all hot and excited at events.  And when it mattered, it would always let you down."

My friend later did some research into his horse's past, and found out, that during his racing days, the horse managed to put two jockeys into the rails.  A few more bad experiences and the said horse was retired from his eventing career.

Now, my friend didn't tell me that Lilly was exactly the same.  He just told me not to waste too much time, if it most obviously wasn't working out.  "A good horse, with a good temperament, should be able to take you from where you are right now, right to where you want to go", he said.

Food for thought.