Choose the correct conjunction to complete the sentence. You may not succeed…

Concept

A conditional conjunction links a possible result to the condition on which it depends.

Unless means “if ... not”: it introduces the condition that must be met to avoid the result stated in the main clause.

Application

Here, success depends on satisfying both requirements: trying one’s best and remaining consistent. Let A mean “try your best” and B mean “remain consistent.” Then “unless (A and B)” means “if not (A and B),” equivalently, “if either A or B is not fulfilled.” The sentence therefore says that failure is possible if either requirement is missing, so unless fits the blank.

Contrast

• When generally introduces a time or situation, as in “Call me when you arrive.”

• While generally introduces simultaneous actions or a contrast, as in “She read while he cooked.”

• Since generally introduces a reason or a starting point in time, as in “Since it was late, we left.”

• Unless introduces an exception or negative condition, as in “Plants wilt unless they receive water.”

Cross-check

Substituting “if ... not” gives the same condition-result relationship: without sincere and consistent effort, success may not follow. Therefore, the completed sentence uses unless.