What percentage of suicides are successful first time round?

Very hard to know: It's almost impossible to definitively know this number. Some accidents are actually suicide attempts, but aren't declared as such. People may withhold this information. Also, not everyone who kills himself leaves a suicide note -- and not everyone who kills himself does so intentionally (accidental drug or alcohol overdoses, etc). Plus you can't interview people who have been "successful.".

Many are not: Most suicide attempts are really just a call for help and "successful suicide" is not the goal. "success" depends on the method, but nothing is absolute and often permanent and sometimes very serious consequences. Even those who suffer severe physical consequences often express that they are glad they did not "succeed" depression is a treatable condition and help is available.