SHAFAQNA (Shia International News Association) – Imam Hussain (AS) mentioned four reasons behind taking an oath.
1. The person has a feeling of weakness or shortage, somehow people do not trust him/her and for attracting the attention of others, he/she takes an oath.
2. The person’s saying is not true, so by taking an oath, tries to strengthen his/her saying.
3. The person is known to others as a liar, so by taking an oath, he/she tries to cover this.
4. The person’s saying is shaky, each time speaks in a different way, and his/her tongue is used to taking oaths .
 Warram Collection, Page 429.