We all eventually get a good feel how comfortable we are as the water gets deeper. I started out about 3-4 decades ago trading two stocks only: KO and MCD. After teaching school all day I rushed off to referee and had time for a quick "meal", burger, fries and a coke. I felt i knew these two stocks. As I started getting past touching my toes in the water I was slowly getting braver. My mottos were two: Take little bites as you go for a 2-3% gain. And the other was if a stock keeps you awake at night then sell it. If you would not buy it here, then also sell it.
Some people try for graduate school before finishing elementary grades.