Stupid issue, but : if you are in a really bad shape and obese, making a push-up (or even something slightly resembling it) is really hard, when simple weightlifting exercises are almost always possible.
Pushups can be made easier by leaning on the wall. Or on a raised platform like the edge of a table or a chair (assuming the platform is stable). They get more difficult the higher the feet are compared to the hands. The culmination is the handstand against the wall.