Those ups and downs of weather are the best reasons I can think of to plant a diverse garden. Even within one species, several varieties will perform differently depending on what they have to go through before harvest.
For monocrop farms, there is crop insurance.
For the gardener, there is depth to the bench. (my sports analogy of the day
Of course, it depends on the size of both the garden and the seed inventory. Seed viability only lasts so long. I run into some problems there each year but I've long been willing to buy more seed than I need for a single season. If I had a tiny garden and limited variety in it, I imagine that I'd have problems sustaining an interest in gardening faced with inevitable disappointments. Maybe ... but, I'd need performance champions.
However: You may never know what results come of your action, but if you do nothing there will be no result. ~ Gandhi
Make everything as simple as possible but not simpler. ~ Albert Einstein