I suppose like your first kiss with a partner and your first day at work I don't think you will ever forget your first sale on Dreamstime.
Similarly, like the most successful holiday you have ever had, the best piece of feedback you ever received or your biggest lottery win you will also have a soft spot for your best selling image.
Then of course, there's the 'odd' ones. Those images that either sell when you were never really thought they would and those that don't sell when you thought they should.
Either way, every day in stock photography is a magical mystery tour that reveals what the world thinks is interesting now and what it believes is 'not yet interesting enough'. Enjoy the journey!