Flat abs may elude you even after following the perfect combination of exercises and diet either because the body fat level needed for flat and toned abs is below the sustainable level matching our present lifestyle or due to the fact that the body fat level is below the bare minimum needed for the body to function in healthy manner. But this should not discourage one from pursuing crunches and exercises.
So, the objective of flat tummy can be materialized through more exercises than your schedule or temperament can handle. This is to be complemented by keener attention to the diet and adhering to it strictly even if the energy level does not allow it initially.
One has to accept that the body functions as a whole unit and not in discrete parts and this realization constitute the stepping stone for embracing the lifestyle focused on achieving flat abs. Even if the dream of flat abs does not materialize, the realization sets in that one isn’t a failure for not reaching the goal.