What sin have I committed that prevents me from performing the Fajr prayer in the mosque, knowing that I use the cold weather as an excuse, even though the weather may not be very cold?

It is permissible for a Muslim to miss congregational prayer during severe cold and wind, based on the hadith of Ibn Umar that the Prophet (peace be upon him) would command people to pray in their dwellings on a rainy or cold night. However, if the cold is not severe, there is no excuse for missing the congregation, and a Muslim must strive against himself and repent with a general repentance that erases all sins. Many people, when repenting, only recall some apparent sins, while shortcomings in inner duties may be more harmful.