I suffer from a lack of motivation, the degree of which is inversely proportional to the amount of work left to do.
In other words, when there's very little left to do, I lose interest.
Why? Probably because once the thing is done, the journey is over. Sure, it's nice to look at, but it really is just another dust collector.
What thrills me is the build - overcoming problems, adding detail, conversions, successfully completing difficult bits......once the final touch is applied, I lose interest.
That's probably why I build so much for other people - I've gotten to build some amazing stuff - that Tamiya 1/16 sclale King Tiger, a couple of Pocher Ferraris (stay away from them - they're awful), 1/48 scale Monogram B-17, B-24, PBY, Verlinden figures.......years worth of work - and nothing to show for it in the display cabinet!! Bugger!