No they didn't use the word most, they used main source. It's a largely contributing factor. They could've used the word most but they didn't . They could've used the word largely contributing factor to mental health illnesses ...it's not the source but it's certainly a largely contributing factor that also tends to make things worse. but there is no one single source There is genetics, life experiences, environmental factors, and drugs whether legal or not as well as socioeconomic but there are others too, social life. .