That’s an old psychological theory that like most psyche theories could have grains if truth but is mostly just yet another unfalsifiable hypothesis. Like babies wanting to bang their mom.

Yeah willpower can be ‘trained’ mostly by not giving into emotional impulse decisions and learning how to say ‘no’ to things you want but dont really need or would actively harm you.

Everyone falls into a spctrum, a few people are ridiculously impulsive to the point of being little more than thoughtless animals living in the moment, a few are ridiculously will powered where they have complete control over themselves but miss out on many fun and spontaneous moments of life due to their need for self control. Most are in the middle, with a bit of a skew towards animalistic impulsivity (that’s usually how babies and families are made)

Most people could use a bit more self/emotional control over impulses, but too much control will rob you of many experiences vital to actually enjoying life.