At the supermarket you don't get much choice of fruit and vegetables. Oh, I know you can buy lots of different fruits - pineapples, oranges, apples, pears, bananas, guavas, passionfruits etc. Vegetables too. But you don't get much choice of varieties of each different type. You might get a choice between Granny Smith, Gala and Golden Delicious [yuk!] apples, and you'll probably get a few choices of spuds as well. But you don't get to choose your own variety of tomatoes, say, or celery, or swede.
It came as a surprise to me that every kind of fruit and vegetable comes in a huge range of varieties to the gardener. The humblest of vegetables - turnips, say - requires you to choose from dozens of cultivars, each with their own qualities of taste, texture, time of ripening, resistance to pests and diseases, preferred soil and climate etc. You get no clue of this shopping at Sainsbury's.
That's because the supermarkets pick their varieties based on qualities that might surprise you. They want produce that is tough enough to survive packing, chilling, transportation and storage, and still look cosmetically blemish-free at the end of a few weeks. Did you ever see tomatoes in the supermarket labelled "grown for flavour" and think "Aren't they all"? The answer is "No". The properties prized by supermarkets are of no interest to the gardener at all, for whom flavour is likely to be paramount, although suitability to our own local conditions is also of interest (and few of us can resist the promise of a "heavy cropper").
If you suspect that those who claim home-grown food tastes better are kidding you, or themselves - you're wrong. It really does taste better, not because it is grown organically (although that's true), not because it's fresher or has travelled fewer food miles (although that's true too), not because knowing you grew it yourself adds self-satisfaction to the culinary experience (although that's certainly true) but because even before the seed was in the ground, it was chosen for its taste.