The quality of a thesis rests on a number of factors. Of these, perhaps none matters as much as what I call the Poke Factor.
Let's back up a bit. The thesis in question here is the one statement that bears the central idea of an expository or persuasive piece in a single, grammatically complete sentence. While descriptive and narrative communication too require a fulcrum, i.e. a statement that pivots the entire unit, both description and narration are personae non grata as far as the CSS English Essay topics go.
As a concept, the Poke Factor (PF) as I define it here, applies only to these two kinds of communication: exposition and persuasion. To be clear, I am using exposition as a blanket term for all sorts of analytical, explanatory and argumentative kinds of writing and speech; and in the term 'persuasion', I seek to include any work aimed at influencing the target audience.
Now, what on earth is PF and why does it matter? To answer the second question first, the Poke Factor matters because you want your essay to matter! If your thesis fails to provoke the reader in just the right way and to just the right degree, your essay will probably fail to sustain their interest. And so to move to the first question, PF describes how the thesis is poised between fact and opinion.
If facticity is one pole of the thesis, 'opinion-ness' is the other. A good thesis is poised between these extremes, often leaning more towards the opinion end of the spectrum. It nudges readers to pick a fight, or at the very least intrigues them enough to want to chew on the essay.
Compare the following three thesis candidates:
a. Education is the basic right of every individual and it is obligatory on the state to ensure that its citizens are adequately educated.
Comment: A big YAWN! We already know the point being made here. It is almost as factual as gravity. If this is the thesis, only a gracious reader would do the favour to read on!
b. Nation-states should urge citizens to seek education on their own instead of expecting the state to provide education.
Comment: As a thesis candidate, this sounds like a ludicrous claim since the logic for the assertion here has not been made explicit. The provocation potency is pretty high here, in fact so high that the seriousness of the matter evaporates into thin air.
c. Major world crises compel the need for pitching formal education less as a program for career building and more as a collective public good, addressing collective global concerns.
Comment: This statement, in comparison to other thesis candidates, is qualified, nuanced and balanced. It calls on a fact, yet at its heart is a compelling point of view with room for some difference of opinion.