Early in my career, someone with authority over me told me to stop reaching. Stay in my lane. Engineers engineer. Leaders lead. Different lanes.
I thanked them.
Not out loud. They would have thought I lost it. But in my head, I started a short list. A list of people who handed me the most valuable fuel a person will ever receive... the fuel of being underestimated.
The list keeps growing
The list has names from school. Names from the Army. Names from Sun Labs, where I worked as a research engineer with a CS degree from a state school in Texas. Names from every step after. Engineering manager. Head of engineering. Author. Keynote speaker at HR conferences across Europe.
Each name on the list represents a moment when someone in a position of authority told me the next step was out of reach. Each name is now a footnote in a chapter I wrote anyway.

Why thank them
Most people hear "you have no business doing this" and feel small. They retreat. They reshape their goals to fit what the doubter said was possible.
Here is the truth... the doubter did you a favor. They told you what they think out loud. Most doubters keep it quiet and watch you fail in slow motion. The loud ones hand you a map. You know exactly which border to cross.
When I wrote Bad Bosses Ruin Lives, more than one person hinted engineers do not write books on leadership. They were wrong. The book exists. The talks happened. HR conferences across Europe brought me out to speak. None of those wins would have hit as hard without those names lined up in my head.
The trick
Do not argue with the doubter. Do not waste a single sentence trying to change their mind. It is a trap. You will lose the energy you needed for the work.
Instead... write the name down. Get to work. Years later, when the thing they said was impossible sits on a shelf or in your inbox or on a stage, you do not need to call them out. You do not need to send a screenshot. You will know. They will know.
Enough.

What I tell my mentees
When an engineer I am coaching tells me their boss said they are not ready for the next role, I ask one question. Do you believe them?
If they say yes, we work on the gap. Real gaps deserve real work.
If they say no, I tell them to write the boss's name down. Then I help them build the case the boss should have seen.
Either way, the doubter served a purpose. They either showed a real gap or they handed over free fuel.
Your list
You already have one. Perhaps you have not opened it in a while. Perhaps you never wrote it down on paper, but you remember every name.
Pull it out. Look at the names. Then look at what you have done since they told you no.
So... what is next on the list?