Crying isn't the goal of this sleep training method, but advocates say it's often an inevitable side effect as your baby adjusts to sleeping on his own. They say the short-term pain of a few tears is far outweighed by the long-term advantages: A child who goes to sleep easily and happily on his own, and parents who can count on a good night's rest.
Thank you for checking out The Baby Sleep Site! I’m sorry to hear you’re having so much trouble with sleep. Based on your comment, it does sound like your little one might be coming into the 4 month sleep regression. We have an article with a lot of information on that here: https://www.babysleepsite.com/baby-sleep-patterns/4-month-sleep-regression/
C.I.O. is the most famous sleep training technique, and the most controversial — although, despite its daunting name, it is safe and effective. In its simplest form, unmodified extinction, you place your infant down at bedtime, drowsy but awake, and then leave the room, without returning to check on or soothe your baby. This method will work quickly, but often produces prolonged periods of crying for a few nights, which can be difficult for parents to tolerate.
Adapt the method to fit your family. If you want to try a method like this but find it too harsh, you can use a more gradual approach. For instance, you can stretch out Ferber's seven-day program over 14 days, increasing the wait every other night rather than every night. Remember your primary objective: To give yourself and your child a good night's rest.