Some implications are easier to prove indirectly.

Contrapositive

To prove

$$P\Rightarrow Q,$$

one may instead prove the equivalent statement

$$\neg Q\Rightarrow\neg P.$$

This is useful when the negation of the conclusion exposes information that is easier to work with than the original assumption.

Contradiction

A proof by contradiction assumes the statement to be proved is false and derives an impossibility.

assume not C
...
derive a contradiction
therefore C

The contradiction might be a statement and its negation, an impossible inequality, or a violation of a known theorem.

Indirect proofs are not weaker than direct proofs. They are alternative logical routes whose usefulness depends on the structure of the claim.