Marinette's guilt is distracting her more than it should leading to her to be a bit careless, and she doesn't know what to do with her overwhelming emotions, but because of this someone sees her in a different light.
After defeating an akuma with chemistry powers, Marinette accidentally got herself blind and gets really scared of how she'll handle her double-life. Even if her miraculous gives her a little vision, she still can't handle her life as Marinette, especially now when Cat Noir visits her every evening. But when she's blind she sees him differently. And her heart almost forgets Adrien.