It varies a lot how hard tyres are to get on and off, and getting the valve core into the hole on some really stiff tyres can be extremely hard, so I understand Paul completely. There are rim protectors in plastic to avoid damaging the rim, and nifty little cable things that screw into the valve core to help get it through the hole, but even then it can be a real struggle, especially if the tyre is old, cold etc, even with tons of tyre fitting gunk. There are lots of tricks and tricks that you learn over time doing it heaps that avoid pinching tubes, and reducing the effort required. There are also pressure pack puncture sealants if you get stuck with a flat, disgusting shit for the poor bastard who eventually fixes it. There are also mobile phones as Paul has mentioned while I wrote this.