But inner reality must be satisfied before outer reality is. That is, if I observe something and decide that it represents my reality of the moment, the "test" that I have applied is not quantifiable because it is not repeatable by another individual. My decision that it meets my standards of reality are completely personal.
Qualitative, personal, experiential, imaginary, internal perception is the source of all meaningfulness.
Quantitative, verifiable, scientific, true, extant, factual reality is necessarily emotionally meaningless.
Intuitively we often conflate what is "real" with what is "meaningful" when actually they are mutually exclusive.
What is real cannot be meaningful (in and of itself) and what is meaningful cannot be real.
The individual who contends that outer reality is the "true" reality sups more from the scientific plate; the claim that inner reality is the "true" reality belongs more to the realm of the philosopher.
Standards of true and false only apply to our "shared external scientific" space where we need to negotiate standards of true and false.
Internal Qualitative experience is not "less true" than shared Quantitative reality. It is simply not held to the same standard (it has no truth value). It is unfalsifiable.
In the same way that "red" is not properly described as "less blue".
It's something else completely.
People can doubt their existence, but it doesn't make them disappear. This makes their belief provably false.
It is however, perfectly valid to doubt one's own meaningfulness.