It's easy to put off the debt incurred from not moving. You don't feel it now so you keep your shoulders hunched and plug away.
You'll move your body later.
If you do this long enough, "later" will come crashing down on you in the form of herniated discs, knee replacements and loss of basic human function.
So, what the hell is movement debt and why is it the most important thing you're not thinking about?
Allow me to explain...
We're all familiar with sleep debt.
If you don't sleep enough one night, you'll feel it, but generally you can still get by. Cut your sleep for more than a few days in a row, however, and it starts to catch up with you. Ignoring it and powering through becomes much, much harder.
Movement debt works the same way.