Compare D&D. You impose disadvantage because you are working in the dark. Your skill is +7 and the DC is 15. You roll a 7 and a 9. So, you failed. But, why did you fail? Because of the darkness? Maybe. After all, it's disadvantage, not a reroll, so, both dice are rolled at the same time, so we cannot know if you would have succeeded if you didn't have disadvantage because you might have rolled that 7. Did the 7 fail because you weren't skilled enough? Well, again, we don't know because you also rolled a 9, meaning you were skilled enough, but, failed. But, you might have failed anyway if there was no darkness because you did actually roll that 7. IOW, there's no actual information. It's all just "make something up".