I've talked about it before, but one thing we all need to acknowledge is that sometimes lifters make very strong associations between certain numbers and how heavy or hard the lift will be. Many people also connect the numbers with how many plates are loaded. That's why so many people want that 315 or 405 lift. For someone who squats 315x5 and 365x1 a 405 squat may seem almost impossible, even as they get stronger. Even when they are strong enough to get the lift, the thought of the number or the look of those 4 plates on each side can be enough to throw them off and keep them from making the lift.
I've had great success overcoming these associations with a couple different methods. For one thing, I train at home and for a while I've only owned 4 45lb plates. For some reason seeing 2 plates, a 35, 2x25's and a 5 on each side is far less intimidating than 4 big ol' plates on each side. Sure, it doesn't look as cool or clean, but it works better than you might think.
Another thing I use is chains. I LOVE accomodating resistance with chains. I've squatted 365 with 80lb of chains twice, which is 445 at the top. But when I look at the bar it still only looks like 365.
Creating a dissonance between how much weight you see and how much weight is actually there is a great way to break those associations I was talking about.