Good eating habit means eating the right kind of food in the right quantity. Similarly, investors also need to invest the right amount towards their goals, i.e., no under or over investing.
A common approach adopted by most investors is to first meet the monthly household expenses and then invest. The approach should instead be 'income minus savings' and what remains should be diverted towards expenses. Also, in the former approach, one mostly invests towards various goals in an arbitrary fashion.