People tend to mimic the behavior of those around them, and characteristics such as smoking, drug use and obesity tend to spread through social networks. But vanDellen’s study is thought to be the first to show that self-control is contagious across behaviors. That means that thinking about someone who exercises self-control by regularly exercising, for example, can make your more likely to stick with your financial goals, career goals or anything else that takes self-control on your part.
So, it is true that circa 1400 years ago when the Prophet Muhammad ﷺ mentioned:
إِنَّمَا مَثَلُ الْجَلِيسِ الصَّالِحِ وَالْجَلِيسِ السَّوْءِ، كَحَامِلِ الْمِسْكِ وَنَافِخِ الْكِيرِ، فَحَامِلُ الْمِسْكِ إِمَّا أَنْ يُحْذِيَكَ، وَإِمَّا أَنْ تَبْتَاعَ مِنْهُ، وَإِمَّا أَنْ تَجِدَ مِنْهُ رِيحًا طَيِّبَةً، وَنَافِخُ الْكِيرِ، إِمَّا أَنْ يُحْرِقَ ثِيَابَكَ، وَإِمَّا أَنْ تَجِدَ رِيحًا خَبِيثَةً
“A good friend and a bad friend is like the perfume-seller and the blacksmith. The perfume-seller might give you some (perfume as a gift), or you might buy some from him, or you might smell its fragrance. As for the blacksmith, he might burn your clothes, or you might breathe in the fumes of the furnace.”
– al-Bukhari, Muslim (lafz is Muslim’s)