I don't think we absolutely know anything.

I do think some of our assumptions have more data points then others, so some things we can be more certain of.

We can use hindsight to generate a probable foresight.

Of course this assumes our senses and the way our brain makes sense of them reflect the world around us with some accuracy and it isn't all an illusion.

I'm also very certain that those who say there is no reality nor no probable objective truth can be caught out by their own actions over something as mundane as a cup of coffee.