Lie to yourself.
I’m still a pretty crappy runner - I can only run a few minutes at a time before I have to slow down to recover a bit and run again, but I’m getting better.
Every time I go to run, I step up onto the treadmill and tell myself that I’ll run for 2 mins straight. This is pretty easy for me and I know I’ll feel fine afterwards, so I run for 2 mins, and I feel fine.
Then I’m like “okay, one more minute then”. And I run for one more minute, by which time I am still good but starting to feel a bit out of breath.
So I tell myself “30 more seconds and I’ll slow down” and after 30 seconds I’m feeling like it would be great to slow down a bit.
But I don’t and I lie to myself again and say “30 more seconds, I can push myself to that”.
And I keep going, and as I feel more and more like I want to stop I say “just a little bit longer” and I decrease it until I’m saying “10 seconds more” and only when I start to really feel like I’ve got to stop do I let myself slow it down for a little recovery.
Apparently I work best with the comfort of a lie behind me.