Happy people don't kill themselves.
I disagree. While undoubtedly the vast majority of suicides are due to severe depression and unhappy people, there are a number of other reasons why people commit suicide. For some, they want to go out with dignity. Others have a debilitating illness and want to be in their right mind when they die rather than die unable to even recognize their own children.
Now that doesn't mean that suicide is the answer or that I condone suicide or anything, merely that there are some people who commit suicide without being really unhappy.
In any formula, constants (especially those obtained from handbooks) are to be treated as variables.