If there were a cause, nirvana would be conditional and impermanent. This means that no amount of effort can produce nirvana, because it does not arise from causes.

If you are practicing with the idea that your effort will engender nirvana, notice that you are still treating it as a special goal to be achieved. In doing so, you are actually reinforcing the grasping that is the defining characteristic of samsara.

Haemin Sunim, Seon monk