Unless you are a complete moron, working hard always beats being smart. Most people have average intelligence.
You know why you are able to sell your work to other people?
Because they are lazy and there simply isn't enough time to learn everything.
You don't need super high intelligence to learn German. (OK German was a bad example, you'll need to be above average :p) It is possible to learn German from the internet for free. Yet, German teachers can make money from teaching German. It is because they worked hard to learn German.
Just by working hard you will never become a millionaire. It's not that easy. The day has only 24h, you can't workd 247/ you will need to relax too, otherwise you will just burnout in a few years. The generation after WW2 is a great example, many of these people worked hard their hole life and still most of them didn't become rich. Dont get me wrong, working hard will make sure you have a good life, but it won't get you into the 1%.
Most of the rich people today either were born with wealth or inherited it later on.
Nice clickbait, OP. Yet, this can be a very interesting conversation. Unfortunately, I am yet to find any "secrets" like you promised. None of the subsequent posters are millionaires themselves so no secrets there either. There are still ways to be a millionaire depending on the society you are from. Being an entrepreneur, taking risk and working is the forumla that everyone knows. There is NO secret about it.
The real secret is that you don't become a millionaire by yourself. Its people and your network that make you a millionaire. A sincere, able-bodies, intelligent, skillful young man with a decent heart can easily become a millionaire if he realizes a few things in time and takes a few right decisions. Yet, most of us are happy, go-lucky idiots at that stage who think that our idealism and hard work is the answer. The answer is making and nurturing connections. Every relation, every connection, every friendship that you make should be made with the view of increasing your net worth. If you connect with the better-off, rich people, you will end up being better.
Yet, most of us spend our times clubbing, drinking and smoking with losers of our own backgrounds. We end up as a bunch of losers self-satisfied in our condition. That, my friend, is the only trap that is stops every young man from becoming a millionaire. That is the real secret. If you are a young, intelligent person in his 20s, make this your mantra. Thank me later. Better still, send me some bitcoin when you are a millionaire.