I find that co-founders affect motivation in a particularly in a good way because while they do keep you moving when you feel glum, there's no pressure to accep

I find that co-founders affect motivation in a particularly in a good way because while they do keep you moving when you feel glum, there's no pressure to accept them as the reason you get up every day, as is the case with working purely for money / an investor somewhere / a boss. It's like the pressure of not wanting to let your co-founder down affects you from the inside out, because you are constantly reminded of your shared fate. They're always there to keep you on your toes, but they don't become a force for extrinsic motivation (which can easily cause stress and deflation instead of adding energy to your inner drive).