Things I know:
1. I exist.
2. My knowledge is imperfect.
3. There are things I can never know.
4. I do not know myself as others know me.
5. My existence will affect the future but not the past.
6. I experience time in a one-way linear fashion.
7. I need only food, water, and a means to control my temperature to live.
8. I will die.
Things I think but cannot know:
1. There is no supernatural God. Our natural environment is all there is.
2. My behaviour is rational.
3. The environment is exactly as I perceive it.
4. Humans perceive their physical environment in the exactly the same way.
But here's an interesting quote from the Wikipedia discussion of epistemology, (the branch of philosophy concerned with the nature and scope and limitations of knowledge), which causes one to wonder if it is really possible to "know" anything:
Suppose we make a point of asking for a justification for every belief. Any given justification will itself depend on another belief for its justification, so one can also reasonably ask for this to be justified, and so forth. This appears to lead to an infinite regress, with each belief justified by some further belief. The apparent impossibility of completing an infinite chain of reasoning is thought by some to support scepticism. The sceptic will argue that since no one can complete such a chain, ultimately no beliefs are justified and, therefore, no one knows anything.
"The only true wisdom is in knowing you know nothing ." (Plato)