Other income streams can come from anywhere and all have various levels of risk even driving a Taxi.
What individuals choose is largely based on interests, passion or comfort (what they know or like).
The way to reduce the risk is to research and learn as much as possible about whatever area you want to earn additional revenues.
Learn about the history, trends, statistics, what can affect your ability to perform successfully (micro) this includes yourself, if you are blind to parts of your personality or mindset.
Then the macro environment, what outside of yourself is a risk to your success, for example; recession, regulatory changes, pandemics, advancement in technology good and bad (Hailo/Mytaxi), social values.
Understand where you are and where you want to be. What do you need to add or improve to help you get there.
These principles apply to everything regarding the business of making money whether a company or sole trader.
What you trade in or on depends on what floats your boat.
The ould 7 P's is a good guide for all ventures. Proper Prior Planning Prevents Piss Poor Performance.
Usually people only learn that after the fact and are burnt out or have no interest in starting again.