Ah, that perfect moment when you have the pattern, the right yarn at the right price, in a colour and texture so lovely you could eat it, and the leisure to cast on right now, row after mesmeric row. Whereas the reality so often is, you pay a fortune for a yarn which is close, but not close enough, to what you had in mind, or, worse, you spot a heap of yarn so cheap you can't pass it up but it's not quite enough for a jumper and far too much for a scarf.
Aged 13, I experienced the perfect moment in knitting my first actual garment. Note the absence of any mention of the pleasure to be derived from finishing, or - my goodness - actually wearing the item. That was some years down the line for me.
I was on holiday with a friend's family on the Isle of Wight when we both decided that sunbathing on the beach was not going to be our thing, hit the yarn shops and I cast on for a top with cutaway shoulders and a huge roll collar, in white with coffee stripes, the collar in coffee too. Doubtless we had seen something along these lines in "Petticoat" or "Honey", which were our style bibles at the time. Curiously, I don't recall ever wearing it, but the satisfaction of casting it on is something I will remember always.