Someone explain what life lines are? pretty please 
Life lines...?
A life line allows you to re-insert your needle in the (sad and sometimes horrifying event) that you drop a stitch or stitches, or like my case, when my 4 yr old just pulled it out. Then you can frog just to your lifeline, and not have to start over.
I am a firm believer in life lines. I’ve had my kiddos pull too many needles out to not use them. Basically, just take a yarn needle with a long piece of yarn, (I use smaller and a different color, sometimes I even use dental floss if I’m using a really light weight yarn) thread it through your stitches, parallel to your needle. Then just keep on knitting. I re-insert it after a repeat (like in lace) or just every few inches.
Hope this helps!
imagine that you make a pattern, you can expect to be difficult (or just a lot of work or you are afraid of toddies around, pets, travel bags… anything that can spoil your fun in keeping the stitches on that needle just fine.)
you can always pull out a needle and frog a few rows. But if you do not frog to the very beginning, there may be a LOT of stitches to pick up. (and you want to pick them up in the right order - not twisted) And it gets harder when you do lace: you may have yo or even multiple yo, stitches that are lifted from a row underneath and all that kind of stuff that is hard to impossible to pick up correctly.
when you have a lifeline, that is easier.
the lifeline gets threaded as explained above: it therefore is a flexible replacement of the needle itself. All stitches are on there. and they are in the right style and orientation. so when you frog, the frogging will naturally stop at the lifeline. you can just run the needle parallel to the lifeline now and catch them all correctly.
lifelines are really helpful.
Gotta love the lifelines! They have many times kept me from stabbing myself (or someone else…)with my needles.
This is the best idea…I started lace knitting and am ready to PULL MY HAIR out, but this will be the better alternative!! Dental floss here i come…
Now I have to find some better needles than i am currently using.
yup, get going with those llife lines. I know about them, never use them, and sometimes make a vow to start with it 
Well, if I will do complicated lace, I will do it. since right now I am making a lace jacket with an easy repeat from thicker cotton, I feel like I can do without (hear me curse over the weekend, I bet).
But good needles are essential. Do yourself a favor and get ones that you really like. In any craft the right tools make SUCH a difference.
With bad needles things come out too tight or lose, they get pulled a lot (I have a pair of plastic needles from somewhere that will ruin any evenness of stitch in NO time) and it is much more efford to work with bad tools, so less fun and a lot less speed.
Thankfully my husband understands that having the same needle size multiple different ways (one or two circulars, at least one set of dpn, maybe two?) is a key to happiness. He does the same thing with his tools selections.
Good needles will leave you a lot more happy! Have fun!