为什么数据绑定并不总是适用于原语？

One of the milestones in learning JS and Angular, is learning that two way data binding with primitives is tricky. If you want to make sure that databinding works, you should always pack it into an object - that is what I was told by some seniors in my company. My question is - why is that happening? What is exactly going on that makes databinding with primitives so compliated in JS?One of the milestones in learning JS and Angula