most of us were puffing and panting by the time we got to the end of the road but can now go there and back without being out of breath !
This ^
I thought I was fit having been a regular at the gym and doing bits of jogging here and there, but my first few times on a bike nearly killed me! But don't worry though because the progression is super fast, within a week I was feeling much less out of breath and a few weeks after that I was doing small hills without having to stop... Good luck and happy cycling!