While the Dominican Rule for the laity is noted for the fact that it's practices are not binding under sin, there is little reason to pledge fealty to a rule, if one does not have some desire to be united to the Order, and accepts that the practice of the rule in the government of life, will assist one in the journey of salvation. That said, circumstances of life may conspire to prevent one from fully living up to the rule, and, while not binding under sin, certainly there is a moral obligation to make the effort, and to have a good reason when the rubber has not met the road, so to speak.
It can be a source of worry if the regular observances are not met, and to grasp how this can be viewed, I'd like to look at our Lord's words in Matthew for a moment:
"You have heard that it was said, 'You shall not commit adultery.' But I say to you, everyone who looks at a woman with lust has already committed adultery with her in his heart."(Mt. 5:27-28)Do you not see how that the intention of the heart, which is the seat of the will, carries the conviction of the act? And that even the act may not carry the intention of the will, and be without merit?
"When you pray, do not be like the hypocrites, who love to stand and pray in the synagogues and on street corners so that others may see them. Amen, I say to you, they have received their reward. But when you pray, go to your inner room, close the door, and pray to your Father in secret. And your Father who sees in secret will repay you."(Mt 6:5-6)I know that even if I had unlimited time and no other obligations, the exact observance of the rule would be difficult, because the intrusion of self-will always is creative enough to find a reason to oppose it; but the vow is made and the resolution, at times weak, still is there. Asking for assistance, the grace to persevere, is the lesson each time by our own strength we find ourselves failing, for the rule is like all other aspects of the Christian life. So like what Jesus says about adultry in the heart, let Jesus find us guilty of desiring to fulfill the rule, even when we have not. And be at peace.