Through our workings of body, speech and mind, we are constantly accumulating three kinds of karmas: virtuous deeds, unvirtuous deeds, or deeds which are neither virtuous nor unvirtuous. So, in order to purify our karma and achieve true happiness, it is necessary to wash off our unvirtuous deeds accumulated in the past, at the same time as we accumulate virtuous deeds.It means to clear off the unvirtuous deeds by positively experiencing the suffering, but the most important point here is to be able to think "my suffering has its cause in myself."

Everybody has virtuous deeds and unvirtuous deeds, and the balance between them defines not only this life but also the next life.

So,

Both processes are necessary: to accumulate hard the virtuous deeds, and to wash off the unvirtuous deeds.