My mnost common mistake is that I make too much... of everything. Two
reasons for this, I think.....

1) I learned to cook for a family of 7 people
2) I have a fear of not having enough, especially when I have guests.

Not such a bad thing. We make good use of the freezer for left-overs.
Some dishes are better cooked in large amounts (like beans, spaghetti
sauce, casseroles, etc) and we make them with the idea of saving some
for future use.

George L