Well worst mistake would be to invest too much time and resource to gambling. Let's face it gambling is a game of chance, there's no guarantee in gambling so making a bet that would either make or break you financially and emotionally would be a very big mistake
Something we all regret. I also never gave any importance to my studies as a student due to gambling ( non btc ) and now regret why i did so. Anyways I have a settled life so yeah when I look back, I feel that was my biggest mistake.
Non technical gambling mistakes we can say such as what you stated.
For a worker it is interfere your work , for a student it is make you looks not smart because gambling is wasting time.
Regret why you did not take study seriously.
Worst mistake to get involve in gambling, put some funds and then it gone.
gambling have high risk since it design to make you lose money and much time.