Yes, you can spend 10% more time to make your app scalable. But assuming your chance of failure is so high, in most cases that extra 10% of time is going to waste. If you spend 10% more time to make all your Minimum Viable Products (MVPs) scalable, but fail 9x, that’s one fewer MVP you could have built.
Why you shouldn’t build an app aimed at 500,000 users in 5 days on a $100 server
Howard Lo
2033

ah, premature optimization is the root of all evil (or at least most of it) in programming