You must fully commit mentally to quitting in order to get through the early days.
It's like going swimming in cold water. You can't just stick a toe in the water and wiggle it around while pondering how badly you want to go swimming. You need to make up your mind before hand then dive right in. The initial shock of the cold water only lasts for a brief period just like the really difficult challenges you experience when first quitting.
Both these things are more of a mental issue rather than physical one; IMO