Opposites signs question?

i have heard that we can sometimes fall back into our opposite signs. i am a scorpio, libra, sagittarius, so i would fall into taurus, aires, gemini. not all at once, but those aspects sometimes change. although i have noticed at times where this has occured, i was windering if someone could fill me in on anything more about this as well as why it occurs. any imput or links would be much appreciated, seeing as google hasnt resolved anything (for once). the reason i ask this, is until i found out about my moon sign libra, i never realized how unoppinionated i can be. i love to debate, yet am unprovoked unless called upon. a desire for a more impulsive and outgoing behavior is what im looking for, and by no means will anything get me there, but astrology has been known to point me into the direction about what i am not noticing about myself.