Yes and No. When Blizzard makes Overwatch or HotS, they have a good initial idea that it is going to be popular because games of similar gameplay already exist

Yes and No. When Blizzard makes Overwatch or HotS, they have a good initial idea that it is going to be popular because games of similar gameplay already exist and popular. On top of that when they play internally and if it is fun, they can be pretty sure that it is going to work. Obviously, if someone like Jonathan Blow is making a completely new game like Witness, then all bets are off.It is basically up to him and people who he trusts with feedback to determine if this is the game worth making. Making Call of Duty version 21 at the same time as close to risk-free as it comes.