The phrase "fundamental flaw" refers to a basic or fundamental mistake or problem in something or someone. It signifies a fundamental error or weakness that can lead to major failures or issues. Full definition
There are a number of fundamental flaws with this game. (snackbar-games.com)
A company that continues to burn through capital while raising more capital to do the same, all while avoiding fundamental flaws in their business model, is a disaster waiting to happen. (goodereader.com)
Recently it was revealed that fundamental flaws in chip design makes every computer vulnerable. (entrepreneur.com)