Look within what you experience as you and realize that all that you are cognizing is manifesting presentially, by appearing, being present in the now. Then, look outwards towards your experience of the world and realize that everything you are cognizing is manifesting presentially here as well.
Even if it wasn’t truly observed by me because I am not the observer, even if the contents of the experience had no more truth than a dream, even if each effort to do so quickly passed out of view, it happened. And that is how I also realized that in happening, these experiences existed. Try falsifying experience for yourself and see if the experience of attempting it doesn’t arise, contradicting your effort.