I agree with this. When I first stepped foot in the Y, I was 18 years old, and, within the first week there I saw a guy benching 405. He was late 30's/early 40's, so at the time I thought he was old, but strong. That was where I got my lifetime goal of benching 405 from. And it was a lifetime goal because I saw him being older, and assumed it might take that long to get there.
Of course, had I stuck with lifting the since then, I'm sure I would have long passed 405, but I got lazy from 20-26 and fell in love with beer and other vices. However, once I started lifting again and learning about powerlifting, I met a competitive powerlifter in my gym and started lifting with him. We only lifted together for about 3 months before I left California, but the impression was set. I wanted to blow this guy's numbers out of the water. I knew there was no limit to my strength (well, obviously there is a limit, but you can't think that way).
The training environment you lift in can play a huge role in your gains. I know it is true for me. I react better, gain better, and train harder when I have someone training with me. It doesn't even have to be someone stronger than me anymore. If I am lifting with someone weaker than me, I still don't want to slack off; I still want to "show-off" I guess.