Sort of related to this...I find that longer rides are more psychologically challenging than physical. My first century I found a group of guys to ride with and it just flew by and I felt great. But riding on my own, anything above 60 miles or so is tough, just because I just get bored and focus too much on how slowly the miles tick off or how hungry I am or how much my butt hurts. So not only will other riders pull you along physically, they pull you along mentally as well.