The better you know your spouse’s history – their upbringing, their schooling, their experiences – the better you can put their behaviors into context. And you can bring up your empathy.
That is not to say that understanding where they come from is to excuse their bad behavior. But it does help you better understand them. It can help you not take some things so personally. You can still not like the behavior, but you understand it better. For example: you can understand why they are so frugal if you understand the financial situation in which they grew up.
You also have a better sense of how you can reverse engineer some of their life experiences. How you can help them in their more vulnerable places.
Listen. Ask. Provide the emotional safety for them to share.