"Je suis assis" vs " je m'assois"

Bonjour seokjiniee,

You may find it helpful, in addition to Cécile's answer, to think of it as follows:-

Imagine that you are showing an old friend a photo of you with classmates at school some years ago.

Your friend has some difficulty identifying you within the various rows of children.

You offer assistance by saying Look, that is me, sat (non-reflexive) just third in from the right on the second row.

Then imagine when you first took your place before the photo shoot  --  you would have in that scenario, sat yourself (reflexive) down in that particular position.

So the issue is that of context. This is the point about whether or not the reflexive form is appropriate.

I hope this helps,

Bonne continuation 

Jim