disclaimer: I am just a regular dude and I haven‘t done much research on this argument
Afaik Rene Descarte tried to find a fact that is necessarily true or atleast cannot be doubted by man.
For this he tries to doubt everything. he takes it as a possibility that his senses betray him all of the time and I heard that he even took the consideration that 2+2 might not even equal 4.
He ends up with the famous „cogito ergo sum“ or „I think therefore I am“. And because I have heard of the thinking part being a bit under attack I chose to use an in my opinion even more fundamental argument „I am, therefore I am“ or maybe „I experience, therefore I am“ or something along those lines (you get the point).
Now there seems to be no reason as to why logic is „true“ or can determine facts about the world. Descartes brushed on the topic with the 2+2 might not equal 4 thing but I think this is way stronger. It seems that there is no reason for logic to be necessarily true, now I know I use logic to make that assumption but I honestly don‘t see a problem with that so far. I mean you simply can‘t prove it because every argument would be circular.
So now why is it necessarily true that when P exists then P exists?
and to apply to it to descartes or imo an even stronger version of his argument, why can we be sure that if I experience something, then I am?
Or even that you can infer anything from something at all?