The first Shia Imam, Ali ibn Abitaleb (AS) said:

O’ servants of Allah (SWT), the one who has better goodwill for himself/herself is more obedient of the Almighty God; and the one who deceives himself/herself more, is the most sinful of the human beings before God. The real loser is the one who deceives himself/herself [1].

[1] Nahjul Balaghah, Sermon 86.

Source: en.shafaqna.com