Well this will be a bit of science then!
I was reading your thread earlier today, and connected with alot of it. I've got myself a 2010 3.0l Z4 (all the creature comforts imaginable, and a good bit of performance), and a 2.0l Zetec Aeroscreen Westie. Since I was 20 (5 years ago), i've had a Porsche924S, 1l Corsa Life, Smart Roadster, VX220 Turbo and the above two. I'm always on Autotrader; and I too am 'finished' as soon as I decide to browse for a new car officially.
Since i've had the westie, a fair few teething issues have taken hold, such as needing to replace the alternator, oil filter leak, indicator failure, electric issues, a stupid woman in a car park not seeing me, and a practical girlfriend (i'm sure some will realise the impact having such a lady in my life). That and everyone saying i'm crazy for having it.
Every fibre in my body is saying I need to sell it before summer, before the price drops for winter and so on. However.... 3 months ago I was saying:
I have never replaced an alternator before in my life.
I have never wired a car before in my life.
I have never done any major modifications to a car before.
I have never bought parts online before for a car.
I dont know the basic mechanical workings of a car before.
I dont know how fragile each area of a car is, such as suspension and steering.
I have never had such stares before in a car.
I have never forgotten to put the oil cap back on, and gone for a drive....
Nowdays I can say yes to every one, and many more. Many lessons learnt for certain! The car makes me want to pull out my hair, and yes, the thought of throwing it on autotrader (or a ditch) has popped into my head. BUT; if I sold it, i'd want to keep tinkering....and I wont be able to tinker with the Z4. I'll go back to being a detailing and polishing OCD chap. I'll pop the bonnet, and stare at it, rather than fiddle. And i'll look to doing modifications that will cost 10x more.
What I have right now, is a toy to play with; a hobby. One that has its ups and downs, like any hobby; and comes with a great community and so on. I've yet to take it on the track, but some roads are absolutely amazing in it.
The day I sell this car, will be to fund a house. And currently, my life isnt there. Hope it isnt for a while longer, purely as an excuse to keep ol' red!
Hope this helps
T