Happy's brilliant plans usually depend on him taking from other people. The basis of the plan, revealed in Act 1, is that-
We form two basketball teams, see? Two water-polo teams. We play each other. It's a million dollars' worth of publicity. Two brothers, see?
What Happy is unable to 'see' is that no-one cares about the loman Brothers. No-one sides with them. The are not popular, well-known or even - in Willy's terms - 'well-liked'. Happy has only ever lived in his brother's shadow. It is Biff who will be expected to put the investment idea to Bill Oliver, and as a thief, Biff has no substance as an investment project.
We see that Happy has inherited his father's misguided optimism and elevated sense of self importance.