Basically what, the title, says. Okay, enough of that, this isn't a joke. If a gun was put to my head and I told to write only using correct comma placement, I would probably survive. The problem is when I am writing I often times see a version of a questionable sentence that I know is right but doesn't flow as well as the one I have instinctively written. And worse, I'm not sure the one I have instinctively written is all that bad in the first place. Here is a short passage for context with a few of these questionable sentences. It all starts with an idea. In most cases a bad idea, but an idea nonetheless. And these ideas, they evolve over time to either cope with their selective pressures or die. This goes on for a while until you’ve got something solid but simple. Practical but expected. Something that wasn’t the original idea at all. Then there’s the exceptions, crazy and terrible, immune to serious consideration. It’s these types of ideas, when they work, that are truly great. Rex’s journal entry (will specify notation later) Rex’s idea was exactly this, a great idea, the best thing since sliced bread, and he knew it. Unfortunately, it had hit a setback much like the idea of sliced bread had so many years earlier. As the story goes, the guy to first slice bread cut his finger open and was sent to the emergency room. Everyone thought he was nuts and no one sliced their bread until the same guy later invented red velvet cake in a similar manner. The first problem is this part: This goes on for a while until you’ve got something solid but simple. Practical but expected. Something that wasn’t the original idea at all. This isn't currently written with commas but does still deal with how to separate clauses and does have commas in some of the edits I tried to make. Practical but expected seems like it isn't a full sentence so I am pretty sure this is wrong right now. This goes on for a while until you've got something solid, but simple, practical, but expected, something that wasn't the original idea at all. That just looks weird. Every edit I make to it looks weird. I have a bad feeling I might have to enter the land of the semicolon where the sun don't shine. Then there's this one: Then there’s the exceptions, crazy and terrible, immune to serious consideration. Sounds fine to me but if I wanted to prioritize correctness over flow I'd make it a little bit different. There there's the exceptions that are crazy, terrible, and immune to serious consideration. One last one: Rex’s idea was exactly this, a great idea, the best thing since sliced bread, and he knew it. If I wanted to make sure it was correct that wouldn't be too hard. Rex's idea was exactly this: a great idea. It was the best thing since sliced bread and he knew it. Except I'm not sure if the colon changes the meaning and I definitely don't like the flow of it as much. I'm not even 100% sure the original is wrong on this one. In short, I didn't listen well in English class and now I don't have enough help from Microsoft word to be able to confidently correct questionable sentence structure. It would mark "A dying, duck." as correct. Yeah, it did. This is something I need to learn so any help is appreciated.
It all starts with an idea. A bad idea, in most cases, but an idea nonetheless. And these ideas, they evolve over time to either cope with their selective pressures, or die. This goes on for a while until you’ve got something solid but simple. Practical but expected. Something that wasn’t the original idea at all. Then there are the exceptions, crazy and terrible, immune to serious consideration. It’s these types of ideas, when they work, that are truly great. (So far so good. I changed around the words in red because it sounds better this way - the other way isn't technically incorrect, but it doesn't flow as well. Since he's writing it in his journal, you could use "there's the exceptions", but it just bugged me.) Rex’s idea was exactly this: a great idea, the best thing since sliced bread, and he knew it. Unfortunately, it had hit a setback much like the idea of sliced bread so many years earlier. As the story goes, the guy to first slice bread cut his finger open and was sent to the emergency room. Everyone thought he was nuts, and no one sliced their bread until the same guy later invented red velvet cake in a similar manner. This one isn't bad either. Just a couple minor things, as noted.
Practical but expected. You're right for thinking that it's technically wrong; it's a fragment, not a sentence. You can totally get away with using fragments on occasion, though. Practical but expected is one of those occasions. Oh, and remember that commas serve as a slight pause in a sentence. If you read a sentence out loud and you feel like you're running out of breath, then you probably need a comma after some clause or another. And if you're still dissatisfied you can split a long sentence into two shorter ones.
There are two issues I think you should address. First, you should brush up on your grammar skills if you feel like you're constantly second guessing yourself. When in doubt, stick to proper grammar when constructing sentences. Second, grammatical "rules" can be broken for stylistic effect, though you should know why you're breaking them and when it's useful to do so. You should reread your passage with those two points in mind. I hope that helps.
