PSA: Gross income unequal taxable income

A topic that has been triggering me as a silent reader for a long time in many discussions in this subreddit is how to deal with the values ​​in the title. Many regulations or limit values ​​currently being discussed relate to taxable income (zvE). In the comments below there are regularly huge waves of indignation about what "Politics"tm could think of to set the values ​​like that. I'm not interested in commenting on whether the amounts/limits are too high