Data science and home assistance general discussion

I’m new to “Big Data” and data science so forgive the simplicity of this topic. I’m not aiming this at the new data science portal although it is what got me thinking about this. My question is what data do we really need to analyze things. Today I think our logs are event based. An event happens and it’s recorded into our databases. We can see how often something happens, but is that really enough to determine “why” it happened. In order to do that wouldn’t we need to also capture the state of every input to the system. For example, the system knows that the exhaust fan in the bathroom was turned on, but what it doesn’t know with that record is that it was turned on because the shower was on and so the humidity needed to be sucked out of the bathroom. We know some of the things that are driving our automations. But what drives the manual events of turning on a light or something. Aren’t those the relationships we are looking for. How do we capture that and the resulting data is I guess why they call it “BIG” data. Am I going down the right track here?