I don't think it's fair to try and make the OP feel bad about this with the very limited information given.
I'm not advising anyone here - just sharing my experience. My LO was waking every hour, would only sleep on someone because of undiagnosed silent reflux. Once this was sorted, they could finally sleep alone as they were no longer in pain, however had become used to frequent night wakings. They were tired and so were we. No one was getting good sleep. Plus, they were crying each night 3-4 times for 15-20 mins while being resettled back to sleep. Did Ferber and the first night did involve crying, but after that second night was minimal and by 3rd night could get through to early hours then a quick feed and back to sleep. My point is, yes there was a lot of crying that first night but we had crying every night before and now none.
I went in and calmed for 2 mins, crying would basically stop and then yes, did start up again as soon as I left. This went on for 1 hour the first night, about 20 mins the next. So for us it really, really worked.
I'd say the most important thing is DO NOT START unless you are willing to see it through. To start and then stop is cruel. To sometimes respond to cries, sometimes not, it's not fair.
Also, a baby will respond to this much better than an older child.
Finally, I would say make sure there is nothing medical as the reason baby is waking up. Rule out anything else first. Make sure they are on an age appropriate routine so are not over or under tired which could be leading to the wake ups. Hopefully, getting routine sorted and if baby is able to fall asleep by themselves at night sleeping won't be necessary. But if it is, stick to it and don't stop.