Don't go be slicing them
As I am lazy, I keep our outdoor Christmas lights up all year. December 1 each year, I plug them in, and set the timer for dusk to 8 hours later.
This year, however, a bunch of the bulbs did not light up, right in the middle of them all -- as my wife quickly informed me. Inspecting it closer, I found it was half a string, precisely. Sixty-bulb LED Christmas lights are built from two half strings of 30 bulbs each.
There was no way I was going to replace the entire string, so I went online to see what kind of solution might present itself. The first several search results made me gag: people actually suggested cutting out the offending half-string and patching in another one. Actually.
I kept searching, and further down the list was a fellow who described in detail how strings of LED lights work, technically. See "LED Christmas Lights and How to Fix Them" by Terry Ritter.
One sentence jumped out at me: the string needs at least 75 volts to light up. That made my brain jump back to my Electricity 8 shop class:
What causes voltage to drop?
What causes resistance?
Corrosion (among other reasons).
I got out some sandpaper and sanded the two dark brown prongs of the plug to a shiny clean brass color. Plugging the lights back into the outlet...
...the lazy lights sprang back on.