In an interview in the Observer last weekend, the director Marianne Elliott – whose revival of Port is currently at the National Theatre and whose production of The Curious Incident of the Dog in the Night-Time shortly opens in the West End – posed an interesting question. "If it is just another run-of-the-mill show, then what is the point?" she asked. "Why bother putting everything into it if you are not producing something that is really worth doing?

It's that attitude that makes Elliott – who was the co-director of War Horse – one of the most exciting directors around, but it also makes me wonder why we're all so accepting of the fact that so much British theatre is run of the mill. The truth is that for every Love Letters Straight from the Heart or Jerusalem or The Passion there are dozens of plays and productions that are merely so-so, neither fantastically good nor particularly bad.

If they were TV shows we'd probably turn them off and do something else, but because we've forked out £40 (or more) and are stuck in the middle of a row, we stick it out and clap politely at the end. It's as if once we've made our choice and invested time and money, we feel the need to justify it to ourselves. I have a friend who often comes out of shows and says, very reasonably: "Oh well. It wasn't so bad."

I recall a Devoted and Disgruntled conference some years ago where somebody called a session to ask why audiences didn't throw rotten tomatoes more often? That would be plain rude, of course: if a production is dull and mediocre it is seldom the actors' fault. But it recognised something about British theatre, I think. Audiences are remarkably forgiving.

Of course there are times when it's right to be forgiving: when a production and all involved risk doing something extraordinary and fall short. Those productions may sometimes be excruciating, but they are seldom run of the mill. But that's not what I'm talking about. I'm talking about yet another tasteful but dull Uncle Vanya revival, or musicals that have been running for a while and everyone is sleepwalking through the show on a wet Wednesday afternoon. If I just wanted to be entertained, I can look at cute cat videos on YouTube for free. I don't have to give up time and money to do that.

In the end I reckon it would do British theatre a world of good if all of us were more honest about its failings as well as its triumphs – whether we're critics, makers or audiences. We need more nights that really blow us away, and make us fall in love with theatre all over again.