Sat at the piano, aged about 10, when I realised that my experience is one of billions and no more real than any other, and that everything we see around us is only so because we say it is so, and that power only exists in the minds of those who witness it.
Nice! "I think, therefore I am" -> is the only thing we can confirm. The rest is our choice to believe a narrative that suits us.
"I think [X], therefore I am [X]" -- whatever you think, and focus your thought and will and desire on is what you create out of yourself.