I read this somewhere (I think it was hardgainer magazine) and this isn't exactly how the story goes but it's to the best of my recollection...
A man walked into a dojo wanting to learn the martial arts. He spoke to the master, and asked:
"How long, if I applied myself, would it take for me to master this art?"
"Ten years," the master said.
"What?! What if I train twice a day, every day, how long will it take me then?"
"Twenty years," the master said.
"What the hell? Okay what if I train all day, every day?"
"Forty years," said the master.
"But why would it take me that much longer to reach my goal?"
"Because," said the master, "with your eyes fixed on the future you are blind to the present."
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In other words, don't worry about benching 400. Just work progressively, and apply yourself, setting lots of small goals to achieve. Maybe one day you'll get there. But if all you think about is wanting to get a 400 lb bench, you'll be too eager, add too much weight, break form, get injured, etc.
I'd like to say that a 300 lb bench press is nothing to scoff at. Most of the people who think that it's not much can't even bench it (see above). How many people do you see in the gym that bench that much? I don't think I've seen one yet.