Just because it is on the market does not mean it will make you rich. It may bring you good additional income, you may break even with your investment, it may flop and not make a dime, or in the rare cases it may make you rich. Remember I said RARE cases.
A license agreement is normally for 3% to 5% of the wholesale price, not the retail price you see in the store. Lets say your invention gets licensed and is selling in the stores for $5. The store probably paid $1 or less for the product. So, you are getting 5% of $1 which is 5 cents on each unit sold. So, if you sold 1,ooo,ooo units your cut will be $50,000. This is a great check, but you are $950,000 short of your first million. So if you are getting $50,000 for every million, you need to sell 20 million units to get your first million. This is before paying the dreaded taxes .
Inventing is a business just like any other business. You need to be realistic in your expectations or you are headed for failure.