The unscripted parts of plays are often the bits we remember.
The forgotten lines, misplaced or misbehaving props, wobbly scenery - while actors strive and search for perfection, more often than not, the whole performance can go awry and be remembered for one tiny plot mishap.
The whole premise of The Play That Goes Wrong, which runs at Sheffield's Lyceum Theatre until this weekend, is based around when everything - and I mean, when everything goes wrong.
The story concerns a local amateur dramatic group trying to stage a 1920s murder mystery play. What we're treated to is a truly hilarious, non-stop cavalcade of razor-sharp gags, slapstick, physical comedy and genuine, hearty laugh out loud moments.
The Mischief Theatre company have created a genuine classic here - and the audience were in absolute stitches from the opening scenes.
To delve too deeply would spoil the show - but there's comedy aplenty in two lung-busting hours where the laughs just keep coming one after the other.
It's fast-paced, frenetic yet delivered with such comic timing that you suspect it is even harder putting on a play where everything is supposed to go wrong than staging one where it isn't.
Props deliberately have to fail, scenery has to do its incorrect job and a seemingly incompetent cast are obviously wonderfully spot on from start to finish in every single scene.
It's quite easy to see from this nationwide tour production why this has been such a smash hit in the West End since 2014.
If you've seen their TV work (Peter Pan Goes Wrong and A Christmas Carol Goes Wrong) you will absolutely adore this show.
It's no word of a lie that at one point, tears of laughing were streaming down my face - and I can't remember the last time a stage or screen comedy did that.
The Play That Goes Wrong is quite simply, brilliantly funny and one of the most inventive, clever and ridiculously hilarious shows ever to hit the stage. You'd be a fool to miss it!