The rest is very good advice, but I take issue with this. Of course you should let people discourage you, just as you should let them encourage you. Putting your hands over your ears and screaming "WORK FIVE DAYS A MONTH MAKE $300K FLY COOL AIRPLANES ALL OVER THE WORLD!!!!" every time someone explains/expresses something that might make you rethink your suppositions is not a good strategy for making a rational decision.
A rational, sound decision is made by acquiring all of the knowledge which is available, then analyzing it through the filter of your own desires, needs, expectations, etc.