I find many trainers{Accomplished ones I know} competed as youth & where good riders, accomplished in their field/discipline & had that horse passion. As they got older they followed down that road & apprenticed with a known trainer,learning ,gaining more responsibilities & starting to get recognition for their riding/training skillls

. From there they stepped out on there own,starting there own training business.
Others I've met :
Some come from a working horse background,start out as ranch hands or grew up with it,something that passed down through family,spend lotsa miles in saddle,break out young colts,after years of day in & out of that they learn alot.After a while they realize their gift of handling horses & start training others

.
Yet Another:
Then there is those that think they are all that & joe trainer .They hang up the trainer sign & act try act the part.Unfortunately there is a few too many of them
No not all trainers are created equal,one should do there homework