Everyone goes through a process when making decisions - It's Friday night: what to wear? who to hang out with? where to go? how best to get there? why be there in the first place? when to meet? what to eat?
Each of the answers to these questions is a decision. Each question also goes through a similar process. We don't notice it because a lot of the answers are automatic. "I look good in red." "Terry's my best friend." "Let's try that old place with the new owners." "I'll drive." "I heard the food was good and we want to go 'out'." "I can be there at 7:30." "I want fish. I want pasta."
But why do you look good in red? How do you know? How long has Terry been in your life and what makes her your 'best' friend? What did you hear about the new menu?
These are the decisions that we take for granted in every day life because in casual conversation we ask "why" a lot. As I've been developing my skills as a writer I am learning that I have to ask those questions (sometimes) before I start writing. The first decision that has to be made is "which of these questions is most important to the story?" and that requires basically answering all of them.
You look good in red because you have fair skin and blue eyes, blond hair and you're not overweight. Your friend Terry goes back to grade school and knows more about you than almost anyone. (Not that any one person really knows you, but that's another story...) The old place with the new owners has gotten good mentions on a website you read and Terry's heard from a couple of other friends that the place is better now. You've been there on dates in the past and it was okay then so you're curious how it's going to be now. 7:30 works for both of you because of your work schedules and gym times, though you don't go as often as you know you should.
To learn more about a character, I ask 'why' again to the answers I just got.
Red is actually your favorite color not just because it's a complimentary color for you but because you associate it with a lot of fun from the old days and you like to give the perception that you're slightly dangerous. Terry was there for a lot of your adventures and if she wasn't she was there to hear about them afterwards. She's trusted you with a lot of things that she doesn't tell anyone else, either. You know she can keep a secret because she knows enough to make your life difficult if she wanted to. Particularly that time at the bar when you --- no need to dwell on that one.
Sometimes I'll go even deeper and ask 'why' again.
You like to appear slightly dangerous because you feel like life is passing you by.
And that begs a whole new set of questions and that's where I find out how my character will make decisions that will affect the story.
So I would encourage you, if you're writing, to ask 'why' as much of your characters as you do in 'real' life. It's the only way to discover more.