Well, the implied volatility is always a factor, but less so the deeper you are in the money and the more correct you are on the direction of price.
I did experience first hand a rather rare implied volatility event last week that surprised even me.
I bought a straddle position on a stock (puts and calls right at the money at the same strike). The stock went up 2% from the place I bought it the same day, and my puts were up 15% while my calls were up 55%, and that's figuring the percentages on the difference between buying at the ask and selling at the bid.
I had never had that happen before.