“It’s a really cool a cappella moment where we get to sing, and the melody is so sick,” Camila Cabello explains while introducing the song. “And if you’re a girl, this song probably relates to you in some shape or form.” It also uses samples from DeBarge's "A Dream," Blackstreet's "Don't Leave" and Tupac's "I Ain't Mad At Cha".
"More than any other song on Reflection, the bitter ballad 'We Know' allows the five girls of Fifth Harmony to display their unique skill sets. After Lauren lets her accusations tumble forward on the pre-chorus, for instance, Dinah is given the baton and belts out the titular hook.", according to Jason Liphutz of Billboard.
"The last song on the album before the deluxe tracks, 'We Know' doesn’t deliver any big melodies or any big-band instruments—but it doesn’t necessarily need it. Just one piano and five melodies, and that works. I love that this song really allows their vocals to shine and deliver a soft yet sultry performance, while lyrically still keeping with the girl-power anthem.", according to Rebecca Mattina of andPOP.
"Their slowest track 'We Know' closes out the standard edition of Reflection. Over minimal production, the group is telling off a player that gets around. I feel like each song on this album really showcases one of the girl’s voices, and this one definitely goes to Lauren. I’ve been a fan of this track after hearing live performances of it, so I’m glad it found a place on the final tracklisting.", according to Marcel Jeremiah of PPcorn.