(1) mathematically
(2) as a finite list of things quantum computers can and cannot do
and most people are not going to understand it mathematically, least of all money people who have to watch and evaluate 10 powerpoint pitches in a day or whatever. Without the math you cannot possibly explain how superposition and entanglement work, and even that explanation requires your audience already understand how classical computers work. So you are often reduced to saying "Here is what we think quantum computers will be able to do. The timeline for accomplishing this is at least a decade out. Here are some other things that people have said quantum computers can do which they definitely will not be able to do." But then you're purely relying on your audience believing you based on your credentials rather than following their own reasoning from a place of understanding. Someone else can come in with different credentials and say different things, motivated by money or simple ignorance mixed with hope, and now your audience is playing the credential evaluation game rather than the quantum computing capability evaluation game. Mix in low interest rates and a few people who have learned what to say to get attention, and you get the current state of things.
There is a quiet core of real quantum computing research happening, surrounded by a moat of noise and hype that is required to interface with investors and the public. My sincere hope is that this quiet core accomplishes real advances before the music stops.