They may believe that they don't deserve any better than to be beaten or raped on a semi-regular basis.Abusers may reinforce this lack of self-worth by saying that abuse is normal, that they are over-reacting, etc.
In this context, victims often rationalize that they aren't really being abused, that their partner really loves them despite being abusive and that makes it okay, that the abuse really isn't all that bad, and other similar statements.
Victims are motivated to generate excuses their abuser, to think of each abuse episode as a "one time" thing (even when it isn't), and to focus on the good aspects of the relationship (particularly those positive things that during the guilt/latency phase of the abuse cycle) and convince themselves that the relationship is really a good one and that everyone has some problems in a relationship, i.e., my partner just occasionally loses his/her temper when really stressed at work, etc.
If they don't threaten to kill or harm the victim or the children, they may threaten to harm themselves, and by so doing, guilt the victim into feeling sympathy for them and then staying to prevent the threatened suicide from happening.
The combination of internal self-esteem deficit, intermittent actual abuse, makeup sex or other positive attention obtained in the wake of abuse episodes, and escalating threats when the victim tries to get away is enough to convince many victims to stay put.
They might say to themselves, "If it was just me, I'd leave this marriage, but my children will be better off coming from an intact home than from a divorced one".
This may not be a rational position to take in all cases; the children may be in fact far more damaged by staying in proximity to an abusive father than they would be by being raised by a single mother.They may be motivated to put up with a lot of spousal abuse because the alternative is to go against the teachings of their church.Still other abused people may rationalize staying in abusive relationships because they think it is the right thing to do for their children.Or for those with poor self-esteem, the rationalizations may be thoughts such as “I don't deserve any better” or “this is the best relationship I've had in my life.” Victims may have any number of low-self-esteem type beliefs that also keep them paralyzed and willing to accept something that is merely "good enough." They may believe that they will be alone forever if they go out on their own.They may believe that they are so damaged that they would only pick another abusive partner anyway so why not stay with this one?If the cycle stopped here and stayed constant, most victims would find it very easy to leave and not endure abuse for long periods of time.