Tomato sauce.
Back when I was just a tadpole, cooking simple things in college, I used to buy Ragu pasta sauce to make with my pasta. When I got to graduate school, I got a little fancier, and I would buy fancy tomato sauce, and I would add diced onions and mushrooms and green peppers, and maybe some pork or chicken or something like that. I tried making my own tomato sauce once, but it just wasn't sweet enough ... and it was too chunky ... and it didn't seem right.
Fortunately, since I moved to the Netherlands I've stepped up my cooking quality, and I make my own tomato sauce now. Sautee garlic and onions (and peppers and mushrooms, if available) in olive oil til they soften, then add a can of peeled tomatoes and mash them up and let it simmer until the tomatoes break down and it all gets, well, saucy. Pretty easy, and super tasty (cuz I put lots of garlic in my sauce). I've been doing that for years, and never considered going back.
But jars of Hak pasta sauce (with veggies) were on sale yesterday, so I bought one and had it with my tortellini. It totally tasted wrong. Very very sweet, very mushy vegetables ... I could see the broccoli, but not taste it. It was good to try it and be reminded of the bad old days of sauce from a jar, but I'll not be buying that again, sale or no sale. I hereby implore my vast readership to experiment with making your own pasta sauce, perfect it, and never again return to the sugary Ragu of your youth.