This is just one of many quotes I was able to find on the importance of investing in yourself. In fact here is another quote from bygone days, that still remains valid.
‘Take a coin from your purse and invest it in your mind. It will come pouring out of your mind and overflow your purse.‘ – Benjamin Franklin.
Investing in yourself not only leads to a financial increase (like when you learn new skills that are more valuable to your employer or enable you to create your own business), but it leads to an increase in the quality of your relationships, the level of your health, and the joy you get to experience in life. So where investing in the share market may increase your financial worth it does not directly impact the quality of your relationships, your health or your daily happiness. That is the realm of ‘self investment’.