First: If you do not have even a small amount of anxiety over your investments, this means that you are not risking enough. You have to have enough money invested in order for you to have real interest. You will make the right decision when you participate in your investments with all your feelings, and then you will be able to monitor this investment and give it greater care.
I am not so sure about this lesson.
Personally, I'd say study with great care what you are about to invest into, and when you finally make the investment, start small. Do not start with an amount that, if lost, you will lose several nights' sleep over it.
I'd say further that interest comes way before you even start pulling out money from your pocket.
What I'd say is that best to start with doing the right analysis, the right research before pouring your money into an investment. And even if you're not sure you could go in it but with a sum small enough that you could be ok with losing. At least this way you get some feedback at not a high expense.