Knitting is done with two points--or more. They can be individual needles or one big circular needle. The point in knitting is to keep all of one row of stitches on the needle(s) at one time.
Crocheting is done with one hook. Generally, you keep one stitch on the hook at a time.
This becomes a critical difference if you have to undo a part of your work because you've spotted an error. It's easy to remove your crochet hook from your work and just rip back to one particular, precise point, stick the hook back into your stitch, and start up again.
Knitting? Not so much. You have to get all those fiddly stitches back on the needle(s), preferably in the right order and with the right twist. You can try to "tink" your work (that's "knit" backwards--basically you unpick one stitch at a time and hook it back on the other point), but it's time-consuming and, if you're knitting cables, it's a nightmare since the whole point of cable stitches is to work the stitches out of order. If you're knitting a four-stitch cable, you don't knit (or purl) 1-2-3-4; you knit (or purl--or both) 3-4-1-2. Fun.
So if you anticipate problems with your knitting, you run a lifeline. At some point in your knitting, when you're sure you've got a "good" row, you run a bit of yarn or thread through all the stitches. Then you keep knitting, knowing that if you have an error you can just unravel your work back to the lifeline, run the needle through the stitches along the line, and pick up your work at that point.
But there's a desire not to run a lifeline. Running a lifeline is an admission that you expect to screw up somewhere, and I didn't run a lifeline on the cabled hat I'm knitting.
The cable pattern is 20 rows long, then you work a repeat of the first 10 rows. I made it successfully through row 20, screwed up row 21, and only spotted my problem when I was on row 25. I spent hours tinking on Sunday night, carefully backing up stitch by stitch and row by row. Supposedly, I only needed to back up a few rows, but when I got to the point where the problem had occurred, I was missing a stitch, and every time I tinked back a row or two more, I wound up short a stitch, or with twisted stitches, or with an unexplained hole. I had run a lifeline after the ribbing, before I started the cables, so I finally just ripped the cables out completely--clear back to the lifeline.
So I've got a new rule if I'm knitting cables: Run a lifeline every fourth row. And leave the lifeline in place until the piece is nearly finished, and periodically examine the cables carefully to make sure they all twist properly. (I have some crochet thread that's too fuzzy for me to use on a doily--I'd get no stitch definition--and it makes for an inexpensive lifeline that doesn't leave yarn fuzzies behind on my knitting.)
I've gotten back through row 18. After all these hours of tinking and reknitting, I'm still not to the point I had reached early Sunday morning. But I will finish this hat, and I will get the cables right.
Yeah. Run a lifeline every fourth row.