Another thing am curious about is, I initially thought that our discretionary income is that money we can afford to lose because it's the money left after all expenses of our basic needs has been taken care of, so I really want to know, how best can we discribe that money we can afford to lose from our weekly or monthly income?
After covering your essential expenses, why you will have left is your discretionary income but however it's not what you can afford to loss because some of the discretionary income is meant to cover things like your entertainment, want or even to invest but however, what you can afford to loss is that part of your discretionary income that you have in which you can spend yet not realise you spent some amount because it has no effect on your survival.
You can have a percentage of your discretionary income to invest which you can possibly consider as an amount you can afford to loss, like 30% and above of your discretionary income you can afford to loss such because you have some good amount left to fix your personal entertainments or lifestyle it if you want to be more aggressive then you can use a bigger percent of your discretionary income or probably cut down your lifestyle expenses like how many bottles of drink you take to a smaller amount to increase your investment.
As long as you can loss an amount and still be fine, having something to lay on when you already lost some is the amount you can afford to loss.