You see your roommate walk in with one single onion, a packet of instant noodles, and that thousand-yard stare. You don't need to be a psychic to know the future.
Textbooks often teach you that will and be going to are basically the same. A coin flip for talking about what's next.
This is a lie.
Be going to isn't about predicting the future. It’s about reporting on the present. You use it when you can see the trail of evidence leading directly to a future event. The seeds have already been planted.
You see the ingredients on the counter. The future is already in motion.
He's going to make instant noodles for dinner again.
Look at those dark clouds. It's definitely going to rain.
I'm going to block his number. I've had enough.
We're going to take a real vacation this year, no emails.
The Arrow Has Already Left the Bow
Think of will as a spontaneous choice made in the moment, like pointing at a menu and saying I'll have the pizza[TRANS]. But be going to means the decision was made long before you even sat down at the restaurant. You've been thinking about that pizza all day. The decision process is in the past; only the outcome is in the future.
This is why be going to feels so much heavier, so much more certain. It connects a past cause to a future effect. It tells the listener that the story has already been written; we are just watching the final scene play out. It’s the difference between "I think this movie might be sad" and seeing your friend reach for the tissues and knowing "Oh, she's going to cry."
The Golden Rule is this: Don't use be going to to guess about the future. Use it when you can already see the future's shadow in the present. Whether it's dark clouds in the sky or a firm decision in someone's heart, the cause is already here.