I think when you are following a horse you have to ask yourself how long do I follow it for?
Personally for me I use a three strikes and your out system and yes I have had them win on say the fourth or fifth time and not bet them that's the way it goes. I suppose another guide would be price IE. If u have backed it eight times and it has not won then the price you obtain should be more than 8/1 as this horse is 25/1 then I would imagine that trainerlayer hasn't bet it more than 25 times so on this occasion it's all well and good backing it, but if it was say 6/4 it would be utter madness to back it whether it wins or not. However people your betting the maths of it all has to come into play.
I’m on today and I’ve backed it several times this season too. Ignore it’s last run and his AW debut was encouraging enough to have a small e/w. Good luck