Any debut novel is usually a case of spitting into the wind - or, just maybe, casting your bread upon the waters. Without an established audience in place, first-time authors have to hope for resonant word of mouth and a receptive reviewer or three.
I suspect that authors who start their careers writing for an adult audience - and who eventually produce a young adult novel or two - are more common than authors who begin by writing for young adults and who then gravitate toward composing something for an adult audience.
The lives of most authors - even, or perhaps especially, the great ones - are necessarily a catalogue of tedious inwardness and cloistered composition. Globe-trotting Hemingways and brawling Christopher Marlowes are the exception, not the rule.