This was essentially me once, but for real. I was running as exercise and discovered that if i slowed down i didn't get nearly as tired and could run much further! I thought i had just had an absolutely genius thought and was really proud of myself. It wasn't until later that i realised that no, i was just being really fucking dumb, as usual.
Not to mention that switching to lighter weights after reaching failure on heavier ones lets you squeeze out a few extra reps that deepen the failure and build more muscle
