"You cannot train a baby to sleep because sleep is a biological function and it is not within our conscious control."
Sleep is as much a biological function as eliminating. While we can help our children learn how to use the toilet, we cannot tell them, "go to the bathroom right now". They may have learned to use the toilet, but they will go when nature calls and there is a physical need to eliminate.
For not only babies, but also adults, falling asleep is not a function we are in control of. You may have experienced this - the harder you try to fall asleep, the harder it actually becomes.
Sleep is influenced by two biological sleep regulators: sleep pressure and circadian rhythm. This is what tells our little one’s bodies that they need to sleep, not a schedule in a book or hours of rocking and bouncing or being left alone in a room to cry so they learn to fall asleep. Sleep pressure builds through the day as they learn and play. Circadian rhythm uses light and darkness to set an internal clock to know when it is time to sleep and time to wake.
Instead, we can also support sleep by having consistent and connection filled routines in place, by tuning into natural rhythms and sleepy cues, by ensuring their environment is conducive to sleep and helping our children feel secure and attached to their caregiver before bed time.