Pain sometimes depends on the ride. Living in Flatlandia, if I do a hilly ride, I will be in some pain and with tight muscles by the end of it. However, there is an important mental component, and knowing you can do it helps a lot.

Same holds true for long flights: once I did a Chicago to Hong Kong direct flight (~16 hours), flights to Europe or South America seem short by contrast. Before, I would start getting really bored and uncomfortable after only 6 hours.