his/her reasons
Pero reconozco que debe haber tenido sus razones.
But I admit he must have had his reasons.
Tom tenía sus razones para para quedarse en Boston.
Tom had his reasons for staying in Boston.
She explained her reasons to us.
State your reasons.
Como dijo A Gui, todo el mundo tiene sus razones.
As A Gui said, everyone has their reasons.
— Kung Fu Sion (2004)
Él tiene sus razones para quedarse allá.
He has his reasons for staying there.