One is at the "passé composé", the other at the "plus-que-parfait".(PQP) The PQP is used to deepen an event in the past, or when an event #1 happens before another event # 2 which is also in the past. line of time: ----> past event #1 ------> (past event #2) --------> present --------- futur ----------> So when you say "je m'étais posé la question", either you asked yourself the question a long time ago, or you asked yourself the question in the past before another more recent past event. Exemple: Tu as déjà été à Londres ? Oui, j'y suis allé l'année dernière, mais j'y étais déjà allé il y a 10 ans. Tu as déjà fait du ski ? Oui, j'en ai fait l'année dernière, mais j'en avais déjà fait quand j'étais enfant. If my answer is not clear, you can google "when do you use the plus-que-parfait" and you'll have more scientific answers.