Only in the first year. Be patient and stubborn and after a few years you will have learned enough about the needs of your plants to grow veggies more reliably and consistently.

I still buy the 'cheap crops' - potatoes, carrots and onions because I'm still not growing enough of these. Everything else, including fresh aromatic herbs every day, comes out of my garden - at the moment it's plenty of tomato and aubergine, cucumbers, courgette and green beans.