A man being sometimes more generous when he has but a little money than when he has plenty, perhaps through fear of being thought to have but little.
Franklin observes that generosity is not always determined by how much money a person has. Someone with limited means may spend or give freely because they fear that caution will reveal their lack of wealth. In this case, generosity is partly shaped by reputation and the desire to appear financially secure.
The remark does not suggest that generosity is generally insincere or that people with less money are especially concerned with appearances. Its broader point is that financial behaviour can be influenced by social perception as well as by actual resources. People may sometimes spend beyond what is prudent to protect their status or avoid seeming poor. Franklin therefore highlights the tension between economic reality and the social pressure to appear prosperous.