It's said that 12% of females can't reach orgasm and 75% don't climax during sex. The reasons for this vary and can be due to medical, physical and psychological.
From a physical point of view one woman may not reach climax due to inadequate foreplay and in particular, clitoral stimulation, or they maybe tired.
Medically speaking, the inability to orgasm can be due to a deficiency in hormones, side effects from medication and surgery to the pelvis.
Many reason for not climaxing is psychological. Some women feel that the act of sex should be special and in their head they think that if the surroundings and situations are not perfect then they cannot orgasm. Some women fail to 'come' due to low self-esteem whilst other women get distracted too easily so can't relax properly.
Pin pointing the reasons for this condition can sometimes be the hardest part. Ways to establish these reasons achieved by talking honestly to their partners or even using a counsellor of GP.