At some point during your love affair with sewing, you will probably have to do some hand sewing. For example, when you want to apply a hook + eye closure.
And when that time comes, you’ll most likely have to begin with a hand needle threaded and with a single or the double thread ends knotted.
This knot ensures that your hand stitching stays put after construction.
Now, the way I was taught involves saliva and a simple hand motion. Yes, you read right: saliva!