I think it's the first good guitar you buy, get, steal or are given. Mine was a 76 Mossman "Flint Hills." I paid $400 for it, and it was worth it, even though it meant not eating for a week.
Then there was the 82 Lowden cutaway -- kind of like a sophisticated city woman after the girl next door dumps you and you go away to college.
And -- yes -- my vintage Telecaster. The guitar that paid the bills. A painted lady and a seducer and a slut, but I loved her. Inevitably she betrayed me -- she let me get old before I could jam with Eric Clapton.
And now, there's the Larravee, the guitar of my old age. Sweet and clean with a conveniently low action for weak, arthritic hands.
I think the L. is the last one, but they were all so dear ...