To hear, we must first be quiet.

Source of Noise can be from objects, surroundings and even human speech. "Noise" too can be from ourself or our own thoughts. Hundreds of thoughts flows in our mind.

Example,

As for today, have you ever remembered how many types of cars you seen today?
Or are most of the drivers that you see today along the roads are females or males?
Most of time, we would only notice a vehicle only if it's unique or maybe perhaps the car almost hit you, and you remembered every detail about that car.

Bottom line is, Just like the cars along the road, cars passing by, if we did'nt pay attention or just did'nt notice anything strange, we would just see cars along the road passing by.

Just like our thoughts, hundreds or maybe thousands of thoughts flow in and out of our mind, only a vivid memory of what it is or what's all about, and then we will forget about it.

"To Hear, We Must First Be Quiet"

If we think too much, we will not be able to focus on the things that happen around us. Thinking too hard is like, keep on worrying about something, panic, stress about something that bothering you, or even thinking out of context.

Have a clear sound mind, like the roads without cars. So if there is a car that passes by, sure you will be able to know. But if there is a road will full of cars, sure it does'nt matter cause there is lots of cars and you will not be able to notice any one of them.

Bottom line is, Keep your mind clear, so if there is any bright ideas, it sure will work.
If your mind if "full" or "stress out", you will not be able to think properly or focus on the problem in hand.