The solo-phase is the moment just before orgasm, when you concentrate on your own feelings.
If you are unable to withdraw attention from your partner and focus on your own feelings for a while it may be hard to orgasm.
This phase is especially hard for girls. That’s why they often cannot orgasm when they make love, while they have no problem coming during masturbation. During sex they pay too much attention to their lover.
Many people fantasize during the solo-phase, because this is an easy way to concentrate.

During intercourse I fantasize. This makes me feel guilty. But if I don’t I won’t come.