There are many traditions regarding this fact that Allah (swt) out of His endless mercy gives us humans a grace where we can build ourselves by controlling our own Nafs (Ammara) only but not the outer obstacle that is the whisper of Shaitan.

Actually human being by nature has two barriers of evil and two strong means of guidance.

Out of two barriers of evil one is his own wild soul ( desire ) or Nafs e Ammara which is the primary and very influential catalyst to leading human towards any evil thoughts and action and the other one is Shaitan. But Shaitan misguides Human only when his own Nafs Ammara gets dominant over his intellect. Therefore in any case it’s our own soul which causes whether we choose right or wrong path then once we have selected any of them, Shaitan’s turn comes and he portrays the things good or bad. If we have decided to do a good deed then Shaitan tries to misguide us that this act of yours is not suitable or not beneficial or not appropriate etc. But when we try to take any wrong decision then same time our Nafs e Lawama ( soul which gives us a feeling of regret that what we are going to do is not good that is our inner guide) at this moment Shaitan comes and portray that evil thing for us in a very beautiful way and tells us don’t listen to your intellect or inner guide and act according to your desire.

Second thing that we have by nature is our intellect with Nafs e Lawama which leads us in every step and tries to guide us towards right path but because in many place our own intellect is also not capable to take a right decision Allah (swt) has sent his revelation that we call Wahi ( Quran and other divine scriptures time to time) with a guide calls them Prophet and Aimmah. So when we are not capable to take right decision with the help of our intellect then Prophet comes and guide us and it doesn’t matter whether it’s the matter of social issues or spiritual issues or political issues or ethical issues etc..
Now in the Holy month or Ramadan Allah (swt) provided this opportunity for us to control our own wild souls (Nafs e Ammara) and He has stopped the influence of Shaitan for a while. And that is why for controlling our Nafs e Ammara Allah(swt) commanded us to first control our desires by Fasting (fasting doesn’t mean we should not eat and drink only but also it tells us to control our eyes from haraam sights, control our tongues from vain talks, it tells our hands and limbs not to do anything which is not good etc..).
Holy Quran tells us:

يَا أَيُّهَا الَّذِينَ آمَنُوا كُتِبَ عَلَيْكُمُ الصِّيَامُ كَمَا كُتِبَ عَلَى الَّذِينَ مِن قَبْلِكُمْ لَعَلَّكُمْ تَتَّقُونَ
O you who believe! fasting is prescribed for you, as it was prescribed for those before you, so that you may guard (against evil).(2:183)

It means by Fasting one can achieve Taqwa ( not going against the commands of Allah and acting according to His commands).
Traditions say when on the Day of Judgement when we will be questioned regarding our deeds and we will blame Shaitan for our mistakes then Shaitan will argue that, “What you did was not because me but because of your own Nafs e Ammara ( wild desires) and Allah had given you inner and outer guides ( intellect and Prophecy with divine commandments) then Human would not be able to deny his acts of evil he had done out of his own material desires.
Therefore if in the holy month of Ramadan anyone does any act of evil it’s because of his own Nafs e Ammara as traditions say.