Why passe compose

Question

"Nous avons joué aux cartes, comme d'habitude"Why do i not use l'imperfait in this sentence. Its a habit? So i use the imperfait?

Accepted Answer

Lexi, the main reference here is to a single ‘event’ of playing cards on the day in question, so passé composé is correct even though it is also ‘part of a habit’. The speaker notes the habit but highlights this ‘episode’
The attached is a very good practical overview of the uses of passé composé and imparfait, with a couple of good simple videos to highlight. 
Clearly, there are ‘rules’ around the use of the 2 tenses, but you will (gradually) develop a feel for which to use in most circumstances. 
Importantly the tense used also conveys meaning - as in this example where the speaker is highlighting that this particular playing of cards was an ‘event’ of note.
 https://www.frenchtoday.com/blog/french-verb-conjugation/passe-compose-versus-imparfait/