There's another factor here, too. If your weather briefing and your estimation of the weather indicated a smooth flight but the flying is bumpy, then the general weather picture you left with is in error. When that is the case, you need to get a new picture. I headed out one day with a rosy picture of the weather and then started hearing pilots up ahead requesting deviations around weather. Because thunderstorms weren't part of my picture, I landed at a nearby airport and did a fresh review of the weather. Storms were there, across my proposed path, but an hour or so later they had moved and I flew on unmolested. When we fly IFR we embed ourselves in the weather, and we feel things that aren't usually there in VFR flying. If there is unanticipated turbulence it comes from one of two things. The clouds are cumulus types with the attendant churning that comes with those clouds. Or, there is wind shear, a change in wind with height or distance. Wind shear is likely associated with a weather system, with the strength of the shear being directly related to the strength of the system. If you weren't ready for this, it means you weren't aware of the system so, again, it might be time to land and regroup. That's how you learn.