The odds are in your favor. The lone egg is a rare, but possible outcome. Sorry to hear about your lonely hatchling. I hope your next nest has better luck! (The odds are in your favor that it will. :-) )
Here's the exact percentage chance to better help see how it works:
When you interbreed 2 dragons of different species, this table is used: A chance at a 5th egg is added because you rolled the dice with species outcome.
- 5 eggs (5%)
- 4 eggs (10%)
- 3 eggs (45%)
- 2 eggs (30%)
- 1 egg (10%)
If you breed two dragons of the same species, this table is used:
- 4 eggs (12%)
- 3 eggs (40%)
- 2 eggs (38%)
- 1 egg (10%)
You're very likely to get 2 or 3 eggs, and you're more likely to get 4 eggs than one. :-) I think it averages out to a little over 2.7 and 2.5 per clutch. The dragon population more than doubles every 15 - 30 days. (depending on cooldown). Single egg nests are supposed to be an occasional and mildly disappointing event. Equally, a five egg nest is supposed to be a rare and exhilarating stroke of luck.