When you're young, you have all these things to worry about - should you go there, what about your mother. And you worry, and try to decide, but then something else comes up. It's much easier to just plain decide. Never mind - nothing is going to change your mind. I did that once when I was a student at MIT. I got sick and tired of having to decide what kind of dessert I was going to have at the restaurant, so I decided it would always be chocolate ice cream, and never worried about it again - I had the solution to that problem.
Whenever I'm at a restaurant, or ordering food for whatever reason, I will check the menu for an item that prominently contains mushrooms. If such an item exists (and it doesn't sound awful or ridiculously expensive), then that's what I'm getting. Decision made.
I started doing this mainly because I like mushrooms, enough that it felt like a really easy way to hand off decision making. It's also good in that, unlike the above, I don't get just the exact same thing every time (although mushroom burgers are starting to seem pretty same-y).
Also reduces the odds that you'll be looking at someone else's plate thinking "I wish I'd have ordered that instead" :)