I can't climax during penetration. It is physical or mental?

About 70% of women who can orgasm in other ways have difficulty reaching orgasm during penetrative sex .Perhaps your husband gives you exactly the right friction and pressure you need during oral sex to make you climax, and when you masturbate, you also know how to bring yourself to orgasm or do you think It can be a mental thing where a woman simply finds it hard to "let go" during full penetrative sex. 
 Whats your thoughts is the problem Physical, mental or both?