Is $T\in \mathcal{L}(V)$ always injective?

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Is $T: V \rightarrow V$ always injective?

My thoughts would be that it is since $V$ is isomorphic to $V$.

There is a bijection. But I feel like I have seen examples where this is not true.

Am I missing something?

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As stated in the comments, $T$ does not need to be injective. However, assuming $\operatorname{dim}V < \infty$, it follows from the nullity rank theorem that $T: V \to V$ is injective iff $T$ is surjective.