Running businesses means to try and predict a lot every day.
Which actually is impossible, because there’s never enough information about the things we need to decide. Often because we cannot afford the time or money required to gather more information.
All we can do on a regular basis is guesstimate. We need to get comfortable using the information we can afford to gather, make the best guess we can and run with it—or decide not to.
Assuming outcomes is only one part of it though. After starting a project based on educated guesses, we need to observe whether the assumptions we made stay true in the real situation.
Then adapt, adjust the course towards the goal. If that proves impossible, kill the project before more damage is done. Move on guesstimating.
"It is difficult to make predictions, especially about the future."
This quote has been attributed to a number of other people as well. I first found the Mark Twain reference, so I’m leaving you with that.