  The study of non-supersymmetric string theories is shedding light on an
important corner of the string landscape and might ultimately explain why, so
far, we did not observe supersymmetry in our universe. We review how misaligned
supersymmetry in closed-string theories leads to a cancellation between bosons
and fermions even in non-supersymmetric string theories. We then show that the
same cancellation takes place for open strings by studying an anti-D$p$-brane
placed on top of an O$p$-plane in type II string theory. Misaligned
supersymmetry consists in cancellations between bosons and fermions at
\emph{different} energy levels, in such a way that the averaged number of
states grows at a rate dominated by a factor
$\mathrm{e}^{C_{\mathrm{eff}}\sqrt{n}}$, with
$C_{\mathrm{eff}}<C_{\mathrm{tot}}$, where $C_{\mathrm{tot}}$ is the inverse
Hagedorn temperature. We prove the previously conjectured complete
cancellation, i.e. we prove that $C_{\mathrm{eff}}=0$, for a vast class of
models.
