In business, “sustainability” means being profitable. Making more money than you spend.
There are different types of money:
- Once-off (investment banks)
- Hourly (audit firms)
- Annuity (insurance companies)
The most sustainable income is annuity-based. Earn while you sleep. Know that when you get a new customer, she will be paying you every month going forward, rather than you have to sell to her again next month, and again the month thereafter.
There is no greater joy than knowing that your revenue is not zero on the first day of the month. All sales build on old sales.
Annuity revenue is what you want. It lets you sleep easy.