"You like to tell stories."
Translation:Fabulas narrare tibi placet.
The verb placere really translates closer to 'to please' or 'to be pleasing to'. The sentence is more literally something like 'Telling stories is pleasing to you'.
The reason we use placet is because the subject of the sentence is fabulas narrare, not 'you'. The act of telling stories is the thing doing the pleasing.
If we use placis is would mean 'you are pleasing'. E. g. nobis placis -> 'We like you.' or 'You are pleasing to us'.