Perhaps the biggest disservice you can do to yourself with regards to achieving your investment goals, is to spend so much time planning your portfolio, so much money building your portfolio and then not monitor it.
Investing is not an end unto itself, but rather a means to an end for most people i.e. investing to buy a home, for retirement or college education. Hence, the need to keep a close tab on your investments. This way you know if you are on track to meet those goals.
It also ensures you know what you own at every time and where it is held and how they are performing.
You’ll want to keep tabs on price, profitability, financial health, and growth prospects. Even changes at the board and management level matter too.