Occasionally, my mac applications end up in a corrupt state where they won’t open. I recently encountered this with Deluge. The first step to diagnose is to open Terminal and open them in the terminal via

Now, the error is more diagnosable but still cryptic. Deluge.app above is a directory and we can navigate to the binary located at Deluge.app/Contents/MacOS/Deluge and execute the actual binary to see a more actionable error

Now, this is something meaningful and Google search worthy. Googling for “Symbol not found: _inflateValidate” takes us to the most likely cause. In my case, uninstall followed by the reinstall of Deluge fixed it.