Towards radical skepticism:
Philosophically, I am a radical skeptic. That is, if we think of "knowing" as meaning certain knowledge, then I don't think there is anything we can know, because all such knowledge is based on observation (which can be faulty), logic (which can be faulty) or faith (which is usually faulty).
How do we know that logic always works?\
Rather than knowing and not knowing, I think we have degrees of sureness. I am very sure that my name is Peter. But not certain. I am pretty sure I will wake up tomorrow. I am reasonably sure that it will rain tomorrow (the forecast right now is at 100% chance, and the forecasts are pretty good for the next day).
Are you certain of anything? What? Why?
There is a large swath of things we have a high enough degree of certainty about to legitimately use the semantic shortcut of saying we know it. And most things we have some degree of uncertainty about, still fit with past experience and the shared experience of others sufficiently that you can plan around them. This is sufficient.
The thing people need more than "radical skepticism" really is "epistemological humility" around things that are ethically or morally ambiguous and exist in complex and unpredictable causal chains. People get over-invested in their ideas and are unable to flex or adjust in response to outcomes.
You can go right back to the whole "I think therefore I am" kind of malarky but in the end, it all works out in the wash. On the one hand, the world is real. On the other, it is an illusion but either way, it fucking hurts when a hammer falls on your foot. So real or not, wear your steel toe-caps
What we perceive through the medium of our senses is subjective, how could it be otherwise? Are we all brains in a vat experiencing a "Matrix" existence? Who knows? Perhaps we're just living in a shared definition of reality. Or, we should, at least, share this reality if we want to survive. Just as our ancestors agreed, for the most part, that the saber-toothed tiger was a threat to be avoided, so should we as a species recognize the threats we face, such as pandemics and climate change.
All knowledge, including what we know today as scientific facts, is provisional, subject to future revision. To assume otherwise is to fossilize our understanding of the universe--a process frequently practiced by religion.
If everything I know is wrong, and I know that everything I know is wrong, then that knowledge is also wrong. So, everything I know is true. The problem arises when I realize that I don't truly know anything beyond the fact that I don't truly know anything. But if I know that, it's wrong.