Hi ! About the Fi number, it seems I had it wrong before seing the course. But can someone precise to me why? Pardon my french in advance if maybe I got something wrong, (litteraly speaking french here). I know I can use the tool on the website, but the way I had calculate it before was by using 400 000$ as an Fi because with a 10% return it would bring me my annual amount needed (40 000$). I know the more it goes and the less return I would have because the equities will be replaced by bonds and 10% is never sure but, that’s what I thought. So I thought I could live with 400 000$ per year. With the course, I actually have to calculate 40 000$ of annual income needed and multiply by 25, which means the right FI number would be 1 million. What is wrong with my way of thinking? Thank you 
It basically comes down to what’s called the “Safe Withdrawal Rate”. 10% may be the average over the last 40 or 100 years, but during that time we’ve had plenty of 5-10 year rough periods that are flat or even slightly down.
So let’s say you have a $400,000 and then the market drops 50% over the next 5 years, leaving you with $200,000. Plus you are also taking out $40,000/year over that time, you go broke! So 10% is not a “safe withdrawal rate”. On the other side of the spectrum, 1% is too conservative because you could just leave your money under the mattress and it would last 100 years. It’s generally accepted that somewhere around 4%-5% is the safe withdrawal rate. That’s where the 25X number comes from (it’s the inverse of 4%).