Motivation fluctuates, but the front line always pushes or holds.
Discipline V: Non-zero-Sum Efforts
My model of discipline is such that a non-zero amount of motivation is required for said discipline to take effect. While I can force myself to do practically anything, they all require some driving force (in the form of motivation) to actually complete.
A few examples:
I go through battles like this on a daily basis, asking myself if I want to do this or that, taking stock of my motivation inventory for each topic, as well as my "general" stock, which can be allocated towards any discipline venture.
And only recently have I begun to realize how volatile motivation is: it changes with no obvious cause (besides energy levels), choosing to be friend one day and foe the next, blocking personal endeavors without explanation one day and supporting them with zeal the next. The sooner this is recognized and accepted, the sooner it can be leveraged to one's advantage and planned for accordingly.
Do not set limits on days where motivation is high. Do not try to save excess motivation in the bank for tomorrow's use, for there are no guarantees it will still be there. Do what you can with it now while it's tangible and in effect.
Too often I see people trying to stretch their supply over a couple of days to be conservative or afraid something might happen if they use all of it. The problem is they think their motivation tank (which has an open top) is leak-tight, that the spout they use to fill their cups won't let any of that precious elixir out while it's closed. But it's not always the spout that leaks. Lack of energy can poke a hole in the container. Lack of expected incentives can poke a hole—even multiple holes if it's multi-faceted—in the container.
And there's no telling when or where these leaks will be coming from. While I'd like to get ample sleep, sometimes there are things that prevent that. While I'd like to see progress in my lifting numbers, sometimes there are things that prevent that. To put more directly, present motivation is vaguely finite and will run out, so use what is available now to fund endeavors.
And to make another analogy: the open top of the container allows refilling, whether through natural means (raining being random bursts of motivation) or artificial (filling being external incentives that increase motivation).
Of course, there are days where motivation wanes and the container is close to dry. It's here that the line must be held and discipline mustered to maintain the progress that has been fought so hard for. The bare minimum is perfectly acceptable: do what's necessary to make sure no steps back are taken. No regression is preferable to regression.
For example, if I lack motivation to exercise I'll only do chin-ups and overhead press to maintain my strength or an hour on the bike to maintain my aerobic capacity. If I lack motivation to do projects at work, I'll only do the monotonous tasks that need to get done, but would sap motivation from my tank. If I lack motivation to go out and do things with friends, I'll call someone and chat for a bit.
The point of this is to do something, anything that keeps the momentum greater than zero.