I’m no expert but I agree it’s definitely mind over matter.
When it starts to slide, or you hit that “I can’t do it” wall slow down, focus on your breathing deeply in and out, and think “just to that bush, and then just to the next lamppost” etc.
I think for beginners it’s not about speed, it’s about building fitness and stamina. I cannot run 5km in 30 mins or less, and personally I think for a lot of us it’s unrealistic. I’d aim for running 5k in any time you can and then improving from that.