The quotation advises against treating expected income as though it were already available. Its practical concern is financial restraint: spending money before receiving it can create obligations that depend on uncertain future resources. The maxim therefore encourages people to base expenditure on what they presently possess rather than on assumptions about what they may earn or receive later.

In Jefferson’s letter to Thomas Jefferson Smith, the sentence appears among a set of practical rules for everyday conduct. Its emphasis is less on economic theory than on personal financial discipline and caution. The advice can be understood as a warning against unnecessary debt, overconfidence and premature spending. It does not rule out all forms of borrowing or investment, but expresses a general preference for keeping expenditure within available means and avoiding commitments that rely on income which has not yet arrived.