Earlier quoted context omitted.
You have about 5 seconds before your brain shuts up those ideas like "I'll definitely exercise more...". It's an awesome idea, life changing even. 5 seconds later your rational self catches up with the idea and starts to counter with 'but I don't have enough time', 'it's too hard', 'maybe tomorrow', etc. The next time you get the idea to exercise more you need to stop what you are doing right then and there and do so…
you need to stop what you are doing right then and there and do something about it If you're at home, there's no reason not to just do 10 pressups right there and then (and as you get better, 20, 30 and so on). Or dips with your chair if you can't do pressups yet.
you need it to be a kind of mediating objective to not lose that pledge. otherwise, the inevitable abandonment comes after exercising a handful of times, if that :P
my intuition tells me you'd need a goal that has pushups (or exercise at all) only as a subcomponent along the path towards the attainment of that goal. hopefully it would persist longer than if solely working out were the goal. so that it doesn't feel "empty" or easily abandon-able after doing it a few times.