I can’t make FB ads work

I’ve uncovered a thought which is affecting my business results. I have a validated offer and I know how to create successful sales funnels. I’ve used Facebook ads on and off with some success, but the last campaign I did the cost per sale meant that the funnel was just breaking even and the margins were very tight. I’ve realized I have a thought “I just can’t make Facebook ads work.” I have an offer that sells and I want to reach a bigger audience. I know that having a profitable lead generation campaign that I can run ongoing is key to this.

C: Facebook Ads
T: I just can’t make them work
F: Discouraged
A: I am not proactive with my ads person. I’ve handed her total responsibility even though my gut is telling me some of the targeting is off. I mentally write off the campaign before properly testing. I say to myself: “this isn’t gonna work.” I don’t give her all the creativity that has gotten results in the past. I envisage a successful business that is generating leads and sales on auto-pilot and I imagine it being out of my reach – like a kid with her face pressed up against the window of a toy store.
R: I am not reaching the audience that I could be, I’m not reaching my sales targets. I’m frustrated and discouraged.

I understand I need to work with the unintentional model before creating my new belief.

What’s the best way to start?