Most health problems have multiple causative factors. Life situations and your body constitution often come together like pieces of a puzzle resulting in a health problem. If you try to hunt down just a single cause, you would hardly succeed. When there is a whole forest of causative factors, isolating just a single tree rarely gives the ultimate result.
The truth is, no disease is ever caused by a single factor, not even by 3 cofactors. There are usually multiple factors and causative agents that each has casual relationship to poor diet, poor immunity, poor health, accumulation of toxins inside the body, negative thoughts, and financial hardship.
A simple health problem such as the flu is not exactly caused only by the flu virus, but by a whole lot more than that. Why did the virus enter your body in the first place? And why was your immune system too weak to kill the virus before it has spread out in your body? Are you more at risk of getting the flu if you are sleep deprived? Are you genetically more susceptible to flu than other people? Think about it!