The commonest failure is not a weak thesis but an absent one. “This essay will discuss the advantages and disadvantages of remote working” announces a topic and commits to nothing, and an essay that opens that way tends to end with “there are arguments on both sides” — which answers no question that was actually asked. The test is mechanical: could a reasonable person disagree with your sentence? If not, it is a description of the territory rather than a position in it.
The second failure is drift. A thesis stated at full strength in the introduction and then quietly qualified in Body 2 leaves an essay arguing against itself, and readers take the last thing they read as your view. This is why choosing the strength is a decision about the whole essay rather than about one sentence: “largely agree” buys you the room to concede that “completely agree” does not, and the concession is usually already planned before the introduction is written.
What a thesis does not need is a preview of your reasons. “I agree for two reasons: firstly cost, secondly time” has spent both body paragraphs before either one exists, and it is mistaken for signposting so often that it deserves naming as the specific error it is.
If nobody could disagree, you have named a topic. “Education is important” is not a position.
“Largely” leaves room to concede. “Completely” does not, and your Body 2 will need some.
Introduction states it, bodies defend it, conclusion restates it. Missing from any of the three and it drifts.
Previewing your two reasons empties the two paragraphs that were going to make them.
