Why is this reflexive?

Question

Nous nous l'imaginons blonde aux yeux bleusCan't you just say "Nous l'imaginons..."

Accepted Answer

Hi Stephanie,
Just to add to Chris' excellent answer, you could use either imaginer or s'imaginer in that example without changing much to the meaning wich is 'concevoir dans l'esprit'. What you think this person looks like in your mind - blond with blue eyes.
S'imaginer is often used for a wrong belief -
Elle s'imagine irrésistible = She thinks she is irresistible 
or in a true reflexive sense as in the following example -
Tu peux t'imaginer la suite = You can guess the rest for yourself 
Hope this helps!

Answer

There's a slight difference in meaning between imaginer and s'imaginer.

imaginer -- imagine
s'imaginer -- to construct ideas about something in one's head which don't necessarily correspond to reality.

In many instances the two are synonymous, but not in all:

Cet écrivain a imaginé cette histoire après avoir séjourné dans tel pays. -- This writer "imagined" that story after having traveled to such a country. In this sentence you couldn't use s'imaginer.

Look here for a bit more on this: https://forum.wordreference.com/threads/imaginer-simaginer.944228/