You know what 90% of my work with parents consists of? Helping them to release the conglomeration of 'shoulds' that they have gathered along the way, which are burdening them like a bunch of barnacles on a ship.
Children should eat three square meals a day.
Children should obey their parents.
Children should have an early bedtime.
Children should be potty trained by age 3.
None of these are universally true, but we often feel like inadequate parents if we can't achieve them! Maybe grazing on nutrient rich foods all day long suits your child's body chemistry better than three square meals. Maybe your child would be better off going to bed at 9:30 and sleeping in until 9 am so she can spend time with her daddy when he comes home from work at 8. Maybe your particular child responds far better to requests than orders or demands.
Who knows what works best for your family? Yep - only you. And how do you know? You experiment. You try different options and see how it goes. Books, other parents, and 'experts' can be a useful source of ideas to experiment with, but nothing can replace your intuition, your connection with your child, and your own experience.
Parenting is a journey, not a destination. It's one big ongoing experiment. We will never get it down to a formula that works in every situation forevermore. It's the flexible willow, not the rigid oak, that survives the storm.
When you let go of all those 'shoulds', you have more resources available to generate strategies that actually work instead of being frustrated that what should work, doesn't! It's okay to lighten up and play with new ideas and see how it goes.