A scientist is meant to be curious. Saying you fully understand something is the opposite.
There are core parts of our understanding that would take a lot of counter evidence to really change. For example, evolution. It's as close to a fact as you can possibly get.
On the flip side, there is always fringe parts of science that we are actively generating new models and theories around.
The problem is distinguishing between the two. Yes, you are an idiot if you think the earth is flat. No, you aren't an idiot if you think that we don't have a full understanding of how the brain works.
Scientific "blasphemy" is making a claim with little evidence that runs counter to the current accepted and working models which have mountains of evidence behind them.
It's the "Let's rewrite the whole system" mentality whenever you encounter a small bug in the software. Scientific understanding is generally a bunch of small fixes and tweaks vs rewriting things ever few years.
So, yes evolution by several forms of selection is pretty well established but by no means do we fully understand how the natural world came to be as it is today. Which is nice if you ask me.
As you say, we are tweaking this theory.