In a hadeeth Rasūl Allāh صلى الله عليه وسلم mentions:
الكيس من دان نفسه وعمل لما بعد الموت والعاجز من
اتبع نفسه هواها وتمنى على الله
It is the inherent nature of the nafs to keep desiring for things. If we keep satisfying our permissible desires (beyond our rights and needs), the nafs will soon become tired of these desires and aspire to other desires which are doubtful until there comes a time when it will eventually desire haraam. We fall into the trap of leaving a desire only for the sake of a new desire. The result is that one’s life becomes a never-ending cycle of new desires and following one’s passions.
However, the only way to reach spiritual heights and gain closeness to Allah سبحانه وتعالى is to sacrifice even the permissible desires. One should sacrifice a desire only for the sake of Allah سبحانه وتعالى and not for the sake of the nafs in the form of a new desire. Only by sacrificing the permissible desires will the nafs remain under control. Either the nafs controls the person or the person controls the nafs.
[This short excerpt is based on a dars entitled 'Talk on the Nafs' held by Shaykh Abu Yusuf Riyadh ul Haq on 7th March 2000].