What were the experimental findings that led to the realisation a  superposition is not resolved until an intelligence looks at the situation ? I am "accepting" Schrodinger's cat - but as the situation is normally presented, an observer has no means of knowing that the outcome has only been determined one way or the other when he looks.

Is there a simpler practically demonstrable effect with, say, electrons or photons.

Is this just too naive a view ? Is it abstract mathematics not based on what can be observed.