Most people don't have to worry about marginal tax rates, right?

I was discussing the common question of "will my taxes be higher now or in retirement" and had a sudden and rather obvious eureka moment: I will never have a marginal tax rate below 22% or higher then 24%. And i think this applies to a huge portion of the country (US): If you're below 22 you're broke, above 24 you're loaded. Yes, rates can change over time, but not in a dramatic predictable way. For planning purposes, you should assume things will stay roughly the same.

Given the level of uncertainty inherent to long term planning based on lifetime career earnings, the difference between 22 and 24 is virtually nil. CONCLUSION: I don't really need to ever concern myself with marginal tax rates. Am i missing something?